I have found the error!
Cause of error: Driver.
I have now tested all the latest drivers.
From version > Adrenalin 24.6.1 (27.06.2024) the problems occur.
No idea what AMD screwed up from then on and whether they will ever fix it.
For all who have similar problems: Up to version Adrenalin 24.5.1 (15.05.2024) everything works fine!
The only thing that bothers me now is that it only boots sporadically with more than 5200 Mhz.
Is this due to the RAM (bad kit), the CPU (bad CPU) or the DeskMini (bad DeskMini?).
As I said, with 6400 Mhz and 1.2V the computer runs like a charm when it boots.
No errors in MemTest86 and no problems in benchmarks.
Can you explain the problem you encountered because I don't see at all what you're talking about? In addition, your account is completely new so I don't see where you would have explained it on this forum, so sorry but what you report seems very vague to me but I would like to understand.