I got the exactly same issue! Any updates on this? I still couldn't nail down the root cause, but the update to 7.1 could be the culprit.
My month so far..
Additional information:
5.15.19-1-pve Kernel, promox 7.1-10 running 2 LXCs and 3 VMs
Seems to always crash around the same time, 2 AM...