I believe I have solved the issue with my rig.
It has been stable for weeks without any issues.
I disabled the XMP profile in the BIOS and that seems to have solved the instability...
Sorry for the late reply, been quite busy...
So I have rebooted the server, still no go, cache seems to be bottlenecking the CPU.
Decided to convert the cache from BTRFS mirror to ZFS mirror and the performance difference is astonishing!
CPU is averaging 3% with 32 docker containers running!
Before, Plex plyers on the local network would freeze at least 5 times when watching a movie -- in direct stream, not transcoded, and now, it is smooth as butter!
Will keep an eye on it but it seems that BTRFS was putting high stress in IOPS and it was bottlenecking the CPU...
Thank you very much for all your help and support with this!
ThanasisPolitis's post in Unraid 6.12.x unstable on my rig was marked as the answer