For reproducing, connect to the router via ssh 10 times, enter in configuration mode and close terminal.
Checked on 1.2.5, 1.2.6-s1, Rolling VyOS 1.3-rolling-202011080217
vyos@r1-1.2.6:~$ ps ax | grep unio 2675 ? Ssl 0:00 unionfs-fuse -o cow -o allow_other /opt/vyatta/config/tmp/changes_only_2654=RW:/opt/vyatta/config/active=RO /opt/vyatta/config/tmp/new_config_2654 2797 ? Ssl 0:00 unionfs-fuse -o cow -o allow_other /opt/vyatta/config/tmp/changes_only_2777=RW:/opt/vyatta/config/active=RO /opt/vyatta/config/tmp/new_config_2777 2919 ? Ssl 0:00 unionfs-fuse -o cow -o allow_other /opt/vyatta/config/tmp/changes_only_2899=RW:/opt/vyatta/config/active=RO /opt/vyatta/config/tmp/new_config_2899 3041 ? Ssl 0:00 unionfs-fuse -o cow -o allow_other /opt/vyatta/config/tmp/changes_only_3021=RW:/opt/vyatta/config/active=RO /opt/vyatta/config/tmp/new_config_3021 3163 ? Ssl 0:00 unionfs-fuse -o cow -o allow_other /opt/vyatta/config/tmp/changes_only_3143=RW:/opt/vyatta/config/active=RO /opt/vyatta/config/tmp/new_config_3143 3285 ? Ssl 0:00 unionfs-fuse -o cow -o allow_other /opt/vyatta/config/tmp/changes_only_3265=RW:/opt/vyatta/config/active=RO /opt/vyatta/config/tmp/new_config_3265 3407 ? Ssl 0:00 unionfs-fuse -o cow -o allow_other /opt/vyatta/config/tmp/changes_only_3387=RW:/opt/vyatta/config/active=RO /opt/vyatta/config/tmp/new_config_3387 3529 ? Ssl 0:00 unionfs-fuse -o cow -o allow_other /opt/vyatta/config/tmp/changes_only_3509=RW:/opt/vyatta/config/active=RO /opt/vyatta/config/tmp/new_config_3509 3651 ? Ssl 0:00 unionfs-fuse -o cow -o allow_other /opt/vyatta/config/tmp/changes_only_3631=RW:/opt/vyatta/config/active=RO /opt/vyatta/config/tmp/new_config_3631 3773 ? Ssl 0:00 unionfs-fuse -o cow -o allow_other /opt/vyatta/config/tmp/changes_only_3753=RW:/opt/vyatta/config/active=RO /opt/vyatta/config/tmp/new_config_3753 3907 pts/0 S+ 0:00 grep unio vyos@r1-1.2.6:~$
It can hang for months.