Just a few points.
1. I like ECC Ram, it almost always logs an error in Event Viewer long before one has trouble with BIOS or Windows.
When I say "long before" I mean Looser Latencies or slower speeds before they show up elsewhere.
2. I am a bit concerned about a 350W power supply and a Ryzen 9 5950X.
How much Amperage does it put out on the 12V line?
3. Run Ryzen Master. Look at its dashboard when you are running light to medium loads.
4. Lastly but don't overlook this.
I am amazed at how many people think that running MemTest64 or Prime95 for hours is the best way to find problems.
Getting your Chip blistering hot and waiting for it to break is only one technique.
Example: I had a system that I would power on and run Prime95 for a Half hour or so, successfully.
But after several successful runs, it would then crash when idling.
Why?
Well when I booted, the chip was cool, running low frequencies with low voltage.
Run Prime95, the frequencies ramp up, so does the voltage and the heat ramps up. But it runs sucessful.
When I stop Prime95, the processor immediately lowers the frequencies and the voltage.
But now the system crashes.
You see the lower voltage was no longer sufficient to go through a Hot chip.
Resistance in Hot chips are higher than in cool chips.
The low voltage was sufficient to power idle when the chip was cool, but not after Prime95
