Unable to connect to L2TP VPN network with Fedora 29

I used to connect to my workplace's VPN network from my F29 laptop. Since last 3 days it has been unable to establish the connection, and so far I am unable to determine what is going wrong on my own. F29 does not report any problem in details. Simply tells me Activation of network connection failed.

Connection type: VPN with IPSec tunnel to L2TP host using PSK. No algorithm specified.

Things I tried:

• Re-creating the connection but it did not work.
• Was able to connect to the VPN in my Android phone from my home network and in my friend's mac from some other network.
• Able to ping the Gateway IP from my F29 (home network).
• Contacted my VPN admin and when I attempted to connect to VPN from F29, he notified me that he did not get any request at all.
• Not sure if this is relevant for the problem, but VPN services like PureVPN still works from F29.

Probably relevant logs:

System version: 5.0.5-200.fc29.x86_64

Using nmcli to list connections and get their UUID:

# nmcli con show
NAME              UUID                                  TYPE      DEVICE    
........................................................................
...............................redacted.................................
........................................................................
TigerIT           f67aaed5-a0c3-454d-8c06-f7efcf03efe8  vpn       --   

The last line is the name of my VPN connection. When I try to connect to my VPN using nmcli, I get the following output:

# nmcli con up uuid f67aaed5-a0c3-454d-8c06-f7efcf03efe8
Error: Connection activation failed: Unknown reason

I looked up for such error, but so far could not find anything that works for me.

Output of journalctl -f when trying to connect:

(I redacted some pluto and network manager's dst logs to keep it a bit shorter)

Apr 10 21:52:18 hyperion NetworkManager[1094]: <info>  [1554911538.3635] audit: op="connection-activate" uuid="f67aaed5-a0c3-454d-8c06-f7efcf03efe8" name="TigerIT" pid=1893 uid=1000 result="success"
Apr 10 21:52:18 hyperion NetworkManager[1094]: <info>  [1554911538.3673] vpn-connection[0x55af17c044f0,f67aaed5-a0c3-454d-8c06-f7efcf03efe8,"TigerIT",0]: Started the VPN service, PID 10846
Apr 10 21:52:18 hyperion NetworkManager[1094]: <info>  [1554911538.3748] vpn-connection[0x55af17c044f0,f67aaed5-a0c3-454d-8c06-f7efcf03efe8,"TigerIT",0]: Saw the service appear; activating connection
Apr 10 21:52:18 hyperion NetworkManager[1094]: <info>  [1554911538.3791] vpn-connection[0x55af17c044f0,f67aaed5-a0c3-454d-8c06-f7efcf03efe8,"TigerIT",0]: VPN connection: (ConnectInteractive) reply received
Apr 10 21:52:18 hyperion nm-l2tp-service[10846]: Check port 1701
Apr 10 21:52:18 hyperion NetworkManager[1094]: Redirecting to: systemctl restart ipsec.service
Apr 10 21:52:18 hyperion systemd[1]: Stopping Internet Key Exchange (IKE) Protocol Daemon for IPsec...
Apr 10 21:52:18 hyperion pluto[10438]: shutting down
Apr 10 21:52:18 hyperion audit[10438]: CRYPTO_IPSEC_SA pid=10438 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:ipsec_t:s0 msg='op=destroy conn-name="f67aaed5-a0c3-454d-8c06-f7efcf03efe8" connstate=8, satype=ipsec-policy samode=transport cipher=none ksize=0 integ=none in-spi=0(0x00000000) out-spi=1365708687(0x1365708687) in-ipcomp=0(0x00000000) out-ipcomp=0(0x00000000) laddr=192.1 exe="/usr/libexec/ipsec/pluto" hostname=? addr=123.49.3.114 terminal=? res=success'
Apr 10 21:52:18 hyperion audit[10438]: CRYPTO_IKE_SA pid=10438 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:ipsec_t:s0 msg='op=destroy direction=initiator conn-name="f67aaed5-a0c3-454d-8c06-f7efcf03efe8" connstate=6 ike-version=1 auth=PRESHARED_KEY cipher=aes ksize=256 integ=sha256 prf=sha256 pfs=MODP2048  laddr=192.168.0.101 exe="/usr/libexec/ipsec/pluto" hostname=? addr=123.49.3.114 terminal=? res=success'
Apr 10 21:52:18 hyperion pluto[10438]: forgetting secrets
Apr 10 21:52:18 hyperion whack[10860]: 002 shutting down
Apr 10 21:52:18 hyperion pluto[10438]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8": deleting non-instance connection
Apr 10 21:52:18 hyperion pluto[10438]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #8: deleting state (STATE_QUICK_I1) and NOT sending notification
Apr 10 21:52:18 hyperion pluto[10438]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #6: deleting state (STATE_MAIN_I4) and sending notification
Apr 10 21:52:18 hyperion pluto[10438]: shutting down interface lo/lo ::1:500
Apr 10 21:52:18 hyperion pluto[10438]: shutting down interface lo/lo 127.0.0.1:4500
Apr 10 21:52:18 hyperion pluto[10438]: shutting down interface lo/lo 127.0.0.1:500
Apr 10 21:52:18 hyperion pluto[10438]: shutting down interface wlp0s20u2/wlp0s20u2 192.168.0.101:4500
Apr 10 21:52:18 hyperion pluto[10438]: shutting down interface wlp0s20u2/wlp0s20u2 192.168.0.101:500
Apr 10 21:52:18 hyperion pluto[10438]: shutting down interface virbr0/virbr0 192.168.122.1:4500
Apr 10 21:52:18 hyperion pluto[10438]: shutting down interface virbr0/virbr0 192.168.122.1:500
Apr 10 21:52:18 hyperion pluto[10438]: leak detective found no leaks
Apr 10 21:52:18 hyperion audit: MAC_IPSEC_EVENT op=SPD-delete auid=4294967295 ses=4294967295 subj=system_u:system_r:ifconfig_t:s0 res=1 src=0000:0000:0000:0000:0000:0000:0000:0000 src_prefixlen=0 dst=0000:0000:0000:0000:0000:0000:0000:0000 dst_prefixlen=0
Apr 10 21:52:18 hyperion audit: MAC_IPSEC_EVENT op=SPD-delete auid=4294967295 ses=4294967295 subj=system_u:system_r:ifconfig_t:s0 res=1 src=0000:0000:0000:0000:0000:0000:0000:0000 src_prefixlen=0 dst=0000:0000:0000:0000:0000:0000:0000:0000 dst_prefixlen=0
Apr 10 21:52:18 hyperion audit: MAC_IPSEC_EVENT op=SPD-delete auid=4294967295 ses=4294967295 subj=system_u:system_r:ifconfig_t:s0 res=1 src=0000:0000:0000:0000:0000:0000:0000:0000 src_prefixlen=0 dst=0000:0000:0000:0000:0000:0000:0000:0000 dst_prefixlen=0
Apr 10 21:52:18 hyperion audit: MAC_IPSEC_EVENT op=SPD-delete auid=4294967295 ses=4294967295 subj=system_u:system_r:ifconfig_t:s0 res=1 src=0000:0000:0000:0000:0000:0000:0000:0000 src_prefixlen=0 dst=0000:0000:0000:0000:0000:0000:0000:0000 dst_prefixlen=0
Apr 10 21:52:18 hyperion audit: MAC_IPSEC_EVENT op=SPD-delete auid=4294967295 ses=4294967295 subj=system_u:system_r:ifconfig_t:s0 res=1 src=0000:0000:0000:0000:0000:0000:0000:0000 src_prefixlen=0 dst=0000:0000:0000:0000:0000:0000:0000:0000 dst_prefixlen=0
Apr 10 21:52:18 hyperion audit: MAC_IPSEC_EVENT op=SPD-delete auid=4294967295 ses=4294967295 subj=system_u:system_r:ifconfig_t:s0 res=1 src=0000:0000:0000:0000:0000:0000:0000:0000 src_prefixlen=0 dst=0000:0000:0000:0000:0000:0000:0000:0000 dst_prefixlen=0
Apr 10 21:52:18 hyperion audit: MAC_IPSEC_EVENT op=SAD-delete auid=4294967295 ses=4294967295 subj=system_u:system_r:ifconfig_t:s0 src=123.49.3.114 dst=192.168.0.101 spi=1365708687(0x51670f8f) res=1
Apr 10 21:52:18 hyperion audit: MAC_IPSEC_EVENT op=SAD-delete auid=4294967295 ses=4294967295 subj=system_u:system_r:ifconfig_t:s0 src=123.49.3.114 dst=192.168.0.101 spi=3823187978(0xe3e1380a) res=1
Apr 10 21:52:18 hyperion ipsec[10863]: warning: could not open include filename: '/etc/ipsec.d/*.conf'
Apr 10 21:52:18 hyperion libipsecconf[10865]: warning: could not open include filename: '/etc/ipsec.d/*.conf'
Apr 10 21:52:18 hyperion systemd[1]: Stopped Internet Key Exchange (IKE) Protocol Daemon for IPsec.
Apr 10 21:52:18 hyperion audit[1]: SERVICE_STOP pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='unit=ipsec comm="systemd" exe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=success'
Apr 10 21:52:18 hyperion systemd[1]: Starting Internet Key Exchange (IKE) Protocol Daemon for IPsec...
Apr 10 21:52:18 hyperion addconn[10869]: warning: could not open include filename: '/etc/ipsec.d/*.conf'
Apr 10 21:52:18 hyperion libipsecconf[10869]: warning: could not open include filename: '/etc/ipsec.d/*.conf'
Apr 10 21:52:18 hyperion _stackmanager[10870]: warning: could not open include filename: '/etc/ipsec.d/*.conf'
Apr 10 21:52:18 hyperion libipsecconf[10872]: warning: could not open include filename: '/etc/ipsec.d/*.conf'
Apr 10 21:52:18 hyperion _stackmanager[10870]: warning: could not open include filename: '/etc/ipsec.d/*.conf'
Apr 10 21:52:18 hyperion libipsecconf[10877]: warning: could not open include filename: '/etc/ipsec.d/*.conf'
Apr 10 21:52:18 hyperion ipsec[11156]: warning: could not open include filename: '/etc/ipsec.d/*.conf'
Apr 10 21:52:18 hyperion libipsecconf[11158]: warning: could not open include filename: '/etc/ipsec.d/*.conf'
Apr 10 21:52:18 hyperion ipsec[11156]: nflog ipsec capture disabled
...
Apr 10 21:52:18 hyperion NetworkManager[1094]: 002 listening for IKE messages
Apr 10 21:52:18 hyperion pluto[11167]: | refresh. setup callback for interface lo:500 24
Apr 10 21:52:18 hyperion pluto[11167]: | setup callback for interface lo:500 fd 24
Apr 10 21:52:18 hyperion NetworkManager[1094]: 002 forgetting secrets
Apr 10 21:52:18 hyperion NetworkManager[1094]: 002 loading secrets from "/etc/ipsec.secrets"
Apr 10 21:52:18 hyperion NetworkManager[1094]: 002 loading secrets from "/etc/ipsec.d/ipsec.nm-l2tp.secrets"
Apr 10 21:52:18 hyperion pluto[11167]: | refresh. setup callback for interface lo:4500 23
Apr 10 21:52:18 hyperion pluto[11167]: | setup callback for interface lo:4500 fd 23
Apr 10 21:52:18 hyperion pluto[11167]: | refresh. setup callback for interface lo:500 22
Apr 10 21:52:18 hyperion pluto[11167]: | setup callback for interface lo:500 fd 22
Apr 10 21:52:18 hyperion pluto[11167]: | refresh. setup callback for interface wlp0s20u2:4500 21
Apr 10 21:52:18 hyperion pluto[11167]: | setup callback for interface wlp0s20u2:4500 fd 21
Apr 10 21:52:18 hyperion pluto[11167]: | refresh. setup callback for interface wlp0s20u2:500 20
Apr 10 21:52:18 hyperion pluto[11167]: | setup callback for interface wlp0s20u2:500 fd 20
Apr 10 21:52:18 hyperion pluto[11167]: | refresh. setup callback for interface virbr0:4500 19
Apr 10 21:52:18 hyperion pluto[11167]: | setup callback for interface virbr0:4500 fd 19
Apr 10 21:52:18 hyperion pluto[11167]: | refresh. setup callback for interface virbr0:500 18
Apr 10 21:52:18 hyperion pluto[11167]: | setup callback for interface virbr0:500 fd 18
Apr 10 21:52:18 hyperion pluto[11167]: forgetting secrets
Apr 10 21:52:18 hyperion pluto[11167]: loading secrets from "/etc/ipsec.secrets"
Apr 10 21:52:18 hyperion pluto[11167]: loading secrets from "/etc/ipsec.d/ipsec.nm-l2tp.secrets"
Apr 10 21:52:18 hyperion NetworkManager[1094]: debugging mode enabled
Apr 10 21:52:18 hyperion NetworkManager[1094]: end of file /var/run/nm-l2tp-f67aaed5-a0c3-454d-8c06-f7efcf03efe8/ipsec.conf
Apr 10 21:52:18 hyperion NetworkManager[1094]: Loading conn f67aaed5-a0c3-454d-8c06-f7efcf03efe8
Apr 10 21:52:18 hyperion NetworkManager[1094]: starter: left is KH_DEFAULTROUTE
Apr 10 21:52:18 hyperion NetworkManager[1094]: conn: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" modecfgdns=<unset>
Apr 10 21:52:18 hyperion NetworkManager[1094]: conn: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" modecfgdomains=<unset>
Apr 10 21:52:18 hyperion NetworkManager[1094]: conn: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" modecfgbanner=<unset>
Apr 10 21:52:18 hyperion NetworkManager[1094]: conn: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" mark=<unset>
Apr 10 21:52:18 hyperion NetworkManager[1094]: conn: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" mark-in=<unset>
Apr 10 21:52:18 hyperion NetworkManager[1094]: conn: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" mark-out=<unset>
Apr 10 21:52:18 hyperion NetworkManager[1094]: conn: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" vti_iface=<unset>
Apr 10 21:52:18 hyperion NetworkManager[1094]: opening file: /var/run/nm-l2tp-f67aaed5-a0c3-454d-8c06-f7efcf03efe8/ipsec.conf
Apr 10 21:52:18 hyperion NetworkManager[1094]: loading named conns: f67aaed5-a0c3-454d-8c06-f7efcf03efe8
...
Apr 10 21:52:18 hyperion NetworkManager[1094]: seeking_src = 0, seeking_gateway = 0, has_peer = 1
Apr 10 21:52:18 hyperion pluto[11167]: added connection description "f67aaed5-a0c3-454d-8c06-f7efcf03efe8"
Apr 10 21:52:18 hyperion pluto[11167]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: initiating Main Mode
Apr 10 21:52:18 hyperion NetworkManager[1094]: 002 "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: initiating Main Mode
Apr 10 21:52:18 hyperion NetworkManager[1094]: 104 "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: STATE_MAIN_I1: initiate
Apr 10 21:52:19 hyperion pluto[11167]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: STATE_MAIN_I1: retransmission; will wait 0.5 seconds for response
Apr 10 21:52:19 hyperion NetworkManager[1094]: 010 "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: STATE_MAIN_I1: retransmission; will wait 0.5 seconds for response
Apr 10 21:52:19 hyperion pluto[11167]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: STATE_MAIN_I1: retransmission; will wait 1 seconds for response
Apr 10 21:52:19 hyperion NetworkManager[1094]: 010 "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: STATE_MAIN_I1: retransmission; will wait 1 seconds for response
Apr 10 21:52:20 hyperion pluto[11167]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: STATE_MAIN_I1: retransmission; will wait 2 seconds for response
Apr 10 21:52:20 hyperion NetworkManager[1094]: 010 "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: STATE_MAIN_I1: retransmission; will wait 2 seconds for response
Apr 10 21:52:22 hyperion pluto[11167]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: STATE_MAIN_I1: retransmission; will wait 4 seconds for response
Apr 10 21:52:22 hyperion NetworkManager[1094]: 010 "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: STATE_MAIN_I1: retransmission; will wait 4 seconds for response
Apr 10 21:52:26 hyperion pluto[11167]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: STATE_MAIN_I1: retransmission; will wait 8 seconds for response
Apr 10 21:52:26 hyperion NetworkManager[1094]: 010 "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: STATE_MAIN_I1: retransmission; will wait 8 seconds for response
Apr 10 21:52:27 hyperion pluto[11167]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: WARNING: connection f67aaed5-a0c3-454d-8c06-f7efcf03efe8 PSK length of 12 bytes is too short for sha2_256 PRF in FIPS mode (16 bytes required)
Apr 10 21:52:27 hyperion NetworkManager[1094]: 002 "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: WARNING: connection f67aaed5-a0c3-454d-8c06-f7efcf03efe8 PSK length of 12 bytes is too short for sha2_256 PRF in FIPS mode (16 bytes required)
Apr 10 21:52:27 hyperion pluto[11167]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: STATE_MAIN_I2: sent MI2, expecting MR2
Apr 10 21:52:27 hyperion NetworkManager[1094]: 106 "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: STATE_MAIN_I2: sent MI2, expecting MR2
Apr 10 21:52:27 hyperion pluto[11167]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: STATE_MAIN_I3: sent MI3, expecting MR3
Apr 10 21:52:27 hyperion NetworkManager[1094]: 108 "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: STATE_MAIN_I3: sent MI3, expecting MR3
Apr 10 21:52:27 hyperion pluto[11167]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: Peer ID is ID_IPV4_ADDR: '123.49.3.114'
Apr 10 21:52:27 hyperion audit[11167]: CRYPTO_IKE_SA pid=11167 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:ipsec_t:s0 msg='op=start direction=initiator conn-name="f67aaed5-a0c3-454d-8c06-f7efcf03efe8" connstate=1 ike-version=1 auth=PRESHARED_KEY cipher=aes ksize=256 integ=sha256 prf=sha256 pfs=MODP2048  laddr=192.168.0.101 exe="/usr/libexec/ipsec/pluto" hostname=? addr=123.49.3.114 terminal=? res=success'
Apr 10 21:52:27 hyperion NetworkManager[1094]: 002 "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: Peer ID is ID_IPV4_ADDR: '123.49.3.114'
Apr 10 21:52:27 hyperion NetworkManager[1094]: 004 "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: STATE_MAIN_I4: ISAKMP SA established {auth=PRESHARED_KEY cipher=AES_CBC_256 integ=HMAC_SHA2_256 group=MODP2048}
Apr 10 21:52:27 hyperion NetworkManager[1094]: 002 "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #2: initiating Quick Mode PSK+ENCRYPT+PFS+UP+IKEV1_ALLOW+SAREF_TRACK+IKE_FRAG_ALLOW+ESN_NO {using isakmp#1 msgid:21e48c60 proposal=defaults pfsgroup=MODP2048}
Apr 10 21:52:27 hyperion pluto[11167]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: STATE_MAIN_I4: ISAKMP SA established {auth=PRESHARED_KEY cipher=AES_CBC_256 integ=HMAC_SHA2_256 group=MODP2048}
Apr 10 21:52:27 hyperion pluto[11167]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #2: initiating Quick Mode PSK+ENCRYPT+PFS+UP+IKEV1_ALLOW+SAREF_TRACK+IKE_FRAG_ALLOW+ESN_NO {using isakmp#1 msgid:21e48c60 proposal=defaults pfsgroup=MODP2048}
Apr 10 21:52:27 hyperion NetworkManager[1094]: 117 "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #2: STATE_QUICK_I1: initiate
Apr 10 21:52:27 hyperion pluto[11167]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: ignoring informational payload NO_PROPOSAL_CHOSEN, msgid=00000000, length=16
Apr 10 21:52:27 hyperion pluto[11167]: | ISAKMP Notification Payload
Apr 10 21:52:27 hyperion pluto[11167]: |   00 00 00 10  00 00 00 01  03 04 00 0e
Apr 10 21:52:27 hyperion pluto[11167]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #1: received and ignored notification payload: NO_PROPOSAL_CHOSEN
Apr 10 21:52:27 hyperion pluto[11167]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #2: STATE_QUICK_I1: retransmission; will wait 0.5 seconds for response
Apr 10 21:52:27 hyperion NetworkManager[1094]: 010 "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #2: STATE_QUICK_I1: retransmission; will wait 0.5 seconds for response
Apr 10 21:52:28 hyperion pluto[11167]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #2: STATE_QUICK_I1: retransmission; will wait 1 seconds for response
Apr 10 21:52:28 hyperion NetworkManager[1094]: 010 "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #2: STATE_QUICK_I1: retransmission; will wait 1 seconds for response
Apr 10 21:52:28 hyperion nm-l2tp-service[10846]: g_dbus_method_invocation_take_error: assertion 'error != NULL' failed
Apr 10 21:52:28 hyperion NetworkManager[1094]: <info>  [1554911548.9644] vpn-connection[0x55af17c044f0,f67aaed5-a0c3-454d-8c06-f7efcf03efe8,"TigerIT",0]: VPN plugin: state changed: stopped (6)
Apr 10 21:52:28 hyperion NetworkManager[1094]: <info>  [1554911548.9674] vpn-connection[0x55af17c044f0,f67aaed5-a0c3-454d-8c06-f7efcf03efe8,"TigerIT",0]: VPN service disappeared
Apr 10 21:52:28 hyperion NetworkManager[1094]: <warn>  [1554911548.9687] vpn-connection[0x55af17c044f0,f67aaed5-a0c3-454d-8c06-f7efcf03efe8,"TigerIT",0]: VPN connection: failed to connect: 'Message recipient disconnected from message bus without replying'
Apr 10 21:52:29 hyperion pluto[11167]: "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #2: STATE_QUICK_I1: retransmission; will wait 2 seconds for response
Apr 10 21:52:29 hyperion NetworkManager[1094]: 010 "f67aaed5-a0c3-454d-8c06-f7efcf03efe8" #2: STATE_QUICK_I1: retransmission; will wait 2 seconds for response
...

I have checked the warnings, those seem to be harmless. I failed to understand why network manager is failing to maintain the connection.

How can I figure out what is going wrong and how can I fix it?

Regarding the "ignoring informational payload NO_PROPOSAL_CHOSEN" error, see the libreswan FAQ for reasons why :

• https://libreswan.org/wiki/FAQ

In the IPsec settings dialog box, try clicking "Disable PFS", this option was added to NetworkManager-l2tp-1.2.12 and was previously disabled. Sounds like your workplace VPN server might not support Perfect Forward Secrecy.