Looking into https://en.m.wikipedia.org/wiki/Serial_presence_detect https://en.m.wikipedia.org/wiki/Serial_presence_detect a bit more after the BIOS upgrade the

Looking into https://en.m.wikipedia.org/wiki/Serial_presence_detect https://en.m.wikipedia.org/wiki/Serial_presence_detect a bit more after the BIOS upgrade the memory is clearly configured at SPD speeds. Maybe A-XMP was previously enabled by the first user (an employee who quit) or the factory. At least on DMI level it looks like that. Why SPD would work less reliably is strange, but as you say complicated stuff is complicated... Enabled A-XMP now and waiting for the next crash (hopefully in vain). Sorry, for the digression. I doubt I have a compromised BIOS, at least I download it from their support and not from any shady source. But the topic made me looking in this problem again, and maybe understand more.