so you are using nested virt? (I think I now remember something in the other thread about the IPs…)
do you have other VMs running in parallel in your proxmox?
my bet would be on something like hitting IO limits or whatever. system not able to read or write properly anymore… mariadb does not has to be the direct cause as @nem already wrote. could simply add to the problem.
do you know what the underlying storage system is on the real hostnode? how did you setup your storage? zfs? thin-lvm? or just plain ext storage?
First screenshot is a kernel panic. Is your microcode up to date? Firmware? Anything tasty in /var/log/boot.log? I’ve seen bad memory for example result in sporadic panics under load. As an example, this line was enough to deduce the memory was bad.