I did an update through the GUI about 10 hours ago and then added a cron job to reboot my BMC since it sucks and crashes about every 24 hours so I set it to reboot it every 12 hours, the only option in the GUI was Reboot, shutdown or something else which I can't remember. About two minutes after I hit save, my server rebooted....and continued to do so for the next half hour or so. It would boot up successfully with no issues, start up everything OMV related, then proceed to reboot about 1.5 to 2 minutes later. I managed to shell in and remove the command from root's crontab...which didn't stop it. Just to make sure I checked the GUI as well as quickly as I could and it didn't...and then it rebooted. I booted into recovery mode and it was stable, so I removed root's cron, admin's cron (the user I was logged into the GUI as) and my own user just for good measure... and that seemed to fix it...until about 10 hours later when it rebooted again.
I'm currently at work, so I can't really look anything up relating to versions since I shutdown my server since it kept rebooting again and my roommate told me my computer was making noise, and it's currently 1 AM.
The only info I could grab is that I'm running 4.18.0-0.bpo.3-amd64 and that my server was stable for weeks (new to OMV) before I updated today, previous uptime was 8 days prior to upgrading the kernel. I'll be able to grab more info when I get home in about 8 hours.