openvpn client connections no more available

Hy, until yesterday I have no problem with openvpn, now my client are no more visible and I can't understand the reason, server.log also with log level = 9 shows no more than this:

Tue Jul 10 07:51:17 2018 us=148398 GET INST BY VIRT: 192.168.2.90 [failed]
Tue Jul 10 07:51:17 2018 us=148403 SCHEDULE: schedule_find_least NULL
Tue Jul 10 07:51:17 2018 us=148409 PO_CTL rwflags=0x0001 ev=6 arg=0x7f32b1565138
Tue Jul 10 07:51:17 2018 us=148414 PO_CTL rwflags=0x0001 ev=7 arg=0x7f32b1565064
Tue Jul 10 07:51:17 2018 us=148419 PO_CTL rwflags=0x0001 ev=3 arg=0x7f32b1565068
Tue Jul 10 07:51:17 2018 us=148426 I/O WAIT TR|Tw|SR|Sw [10/0]
Tue Jul 10 07:51:17 2018 us=158882 PO_WAIT[1,0] fd=7 rev=0x00000001 rwflags=0x0001 arg=0x7f32b1565064
Tue Jul 10 07:51:17 2018 us=158922  event_wait returned 1
Tue Jul 10 07:51:17 2018 us=158929 I/O WAIT status=0x0004
Tue Jul 10 07:51:17 2018 us=158937  read from TUN/TAP returned 60
Tue Jul 10 07:51:17 2018 us=158947 GET INST BY VIRT: 192.168.1.175 [failed]
Tue Jul 10 07:51:17 2018 us=158952 SCHEDULE: schedule_find_least NULL
Tue Jul 10 07:51:17 2018 us=158959 PO_CTL rwflags=0x0001 ev=6 arg=0x7f32b1565138
Tue Jul 10 07:51:17 2018 us=158964 PO_CTL rwflags=0x0001 ev=7 arg=0x7f32b1565064
Tue Jul 10 07:51:17 2018 us=158968 PO_CTL rwflags=0x0001 ev=3 arg=0x7f32b1565068
Tue Jul 10 07:51:17 2018 us=158976 I/O WAIT TR|Tw|SR|Sw [10/0]
Tue Jul 10 07:51:17 2018 us=334932 PO_WAIT[1,0] fd=7 rev=0x00000001 rwflags=0x0001 arg=0x7f32b1565064
Tue Jul 10 07:51:17 2018 us=334972  event_wait returned 1
Tue Jul 10 07:51:17 2018 us=334980 I/O WAIT status=0x0004
Tue Jul 10 07:51:17 2018 us=334988  read from TUN/TAP returned 60
Tue Jul 10 07:51:17 2018 us=334997 GET INST BY VIRT: 192.168.1.175 [failed]

how can I understand where's the problem? Thanks, Antonio