Hi,
This doesn’t seem as Virtualmin related.
Few tips:
- Check the status of those sessions by running
loginctl session-status ID; - Check and investigate on those active connections by running
journalctl -xe |grep session; - Check
/etc/systemd/system.conf, probably something got mis-reconfigured.
Did you try locking down the access to the system in different ways to find out under which circumstances it could stop?
Those are just the tips, and it doesn’t seem as Virtualmin issue and should be asked some place else.