Alright... That's clear and thanks for helping me analyse, very new to the whole XCP-ng environment (and Linux in general)
/var/crash does not have anything in the folder
What I mean by lock up, is that it indeed stops responding to anything.
No more SSH, router doesn't show system in devices anymore, none of the VMs respond, no display on the screen attached to the machine, no input recognised from the keyboard.
The Power LED is still on and the fans are whirring so the machine stays powered on in any case.
I'll check in the BIOS for the C-states at least, the BIOS firmware itself is the latest version so if that doesn't help I guess I'm out of luck for now...