First I would check hardware problems. Run memtest86+ to check your RAM. Check your disks with smartctl long selftests (but usually you then also should find IO errors in the syslog). Replace the PSU in case you got a spare one. Remove CPUs from sockets and add them in again in case not all pins got a good contact and low heat expansion breaks contacts.
Then I would check if the BIOS is on the latest version. Upgrade PVE to the latest version, in case you didn't upgraded for some time and maybe also try some new opt-in kernels or older kernels.
PS:
kern.log and syslog can't be opened.