I think I can finally say I have a stable system once again. After the RMA replacement of my Ryzen CPU to fix the “Performance Marginality Problem” I noticed that I was still getting some regular system lockups/freezes when it was left idle.
How long this secondary issue has been present I am unsure. Over the summer I had been using the machine but turning it off after use as it was keeping the room a little too warm. I probably didn’t notice the idle issue as I wasn’t leaving it idle. Any occasional occurrences of problems I attributed to the old CPU.
The current workaround has been to disable the C-States in the BIOS. It appears when the system is idle it is going into a low power mode but for some reason this isn’t happening correctly. At this time I’m unsure if this is related to the BIOS itself or Fedora 26 running a 4.13 kernel.
I have upgraded both BIOS (AGESA 126.96.36.199b) and kernel over the past few months so I will have to test again when one of them changes. Next week Fedora 27 is released, it will likely ship with a 4.13 kernel but 4.14 should follow shortly after. A BIOS with AGESA 188.8.131.52 might arrive before the end of the year.
For the time being I will settle for a little additional power usage and no crashing.