Users not able to connect to VPN with DCO enabled and strange log line in openvpn.log

[bamypamy]

Hey, I have enabled DCO for a new VPN some time ago and everything seemed to be working fine.
Yesterday all of a sudden users where not able to connect to the DCO enabled VPN anymore for about 30 minutes.
During these 30 minutes connections to other VPNs on the same Firewall without DCO were successful.
It worked again without me changing anything.

There is nothing in the logs during this time besides these log lines which started to appear after I enabled DCO and are logged twice every time a users logs in to the DCO VPN.

openvpn[45927]: Failed to get peer stats: No space left on device (errno=28)

There is plenty of space left on the device.

Filesystem                            Size    Used   Avail Capacity  Mounted on
pfSense/ROOT/default                  202G    1.3G    201G     1%    /
devfs                                 1.0K    1.0K      0B   100%    /dev
pfSense/tmp                           201G     11M    201G     0%    /tmp
pfSense/var                           201G    3.4M    201G     0%    /var
pfSense/home                          201G    4.5M    201G     0%    /home
pfSense/cf                            201G    128K    201G     0%    /cf
pfSense                               201G     96K    201G     0%    /pfSense
pfSense/var/log                       201G    3.6M    201G     0%    /var/log
pfSense/var/db                        201G    4.7M    201G     0%    /var/db
pfSense/var/cache                     201G    104K    201G     0%    /var/cache
pfSense/var/tmp                       201G    136K    201G     0%    /var/tmp
pfSense/reservation                   224G     96K    224G     0%    /pfSense/reservation
pfSense/ROOT/default/cf               201G     20M    201G     0%    /cf
pfSense/ROOT/default/var_cache_pkg    201G    309M    201G     0%    /var/cache/pkg
pfSense/ROOT/default/var_db_pkg       201G    3.4M    201G     0%    /var/db/pkg
tmpfs                                 4.0M    152K    3.9M     4%    /var/run
devfs                                 1.0K    1.0K      0B   100%    /var/dhcpd/dev

Any idea if this is connected to DCO and what these log lines are?

Update: I forgot one thing. The firewall is set to use two NTP servers that are reachable, and one was also showing as active, but the time drifted back about an hour on the firewall.
I disabled and reenabled NTP Service and the time was correct again. I did that two hours after the VPN had already started to work again. Did not see that before.

Update2: Running Version: 23.05.1-RELEASE on a Netgate 7100 in a two node cluster.