Hi all !
Problem is solved: in the end, the RAM I had originally installed was causing all the errors.
The original RAM was an "old" 2x4Go 2133MHz. I guess the timing was incompatible with Intel 12th Gen CPUs, because all MEM tests I ran returned errorless.
I ordered a new 16Go stick, 3200MHz, and the server has been running flawlessly for 1 continuous month. I never had this stability before!
