Samba CIFS mount only works after SSH connection to samba server

CIFS mount of my remote samba share for some reason unmounts from client in the middle of nowhere and doesn't mount back (log below) until I do an SSH connection from client to server, which, for some reason - fixes everything until random unmount again

Status code returned 0xc0000001 NT_STATUS_UNSUCCESSFUL
 CIFS VFS: Send error in SessSetup = -5
 CIFS VFS: cifs_mount failed w/return code = -5

At first I thought that it could be DNS or routing issue, (although, server can be traced and pinged both by address and hostname) I added static entry for server in client's hosts but, apparently, no luck there

Problem persists only on a single specific client with default, clean CIFS/Samba installs on CentOS 5.11

Client versions: samba 3.0.33-3.41.el5_11, cifs-utils 5.9-93.3

Server: cifs-utils 2:6.4-1ubuntu1.1, samba 2:4.3.11+dfsg-0ubuntu0.16.04.31

Mounted via fstab like this: //hostname/sharefolder /mnt/mountfolder cifs user=,password=,sec=ntlm 0 0

Would be grateful for any ideas where to dig from here