Hello @FranzB , I saw this thread and Since I have a 3960x with Aorus Master board I went ahead to test Prime95.
I currently can’t reproduce any issue with Prime95 under Windows 10 or Server 2019 (I have a dual boot system). My BIOS version is F5c
However, I tried a live Ubuntu Linux 20.04 and downloaded Prime95. I started to perform the torture test but after all threads are started I am getting a “killed” message on the terminal window. Doesn’t seems to be related to the issue you have but maybe an issue with using Ubuntu Live.
Unfortunately, Ubuntu 20.04 runs with Kernel 5.4, and only the newer Kernel 5.6 fully supports the Ryzen 3000 series power states, and PBO system. I can see that currently Ubuntu defaults to the lower PState (2.200 Mhz). So I decided not to install Ubuntu on one of my hard drives. I can also see a lot of ACPI errors under linux on boot (Oddly looks like Ubuntu supported as declared on the AMD’s CPU page is false)