I've been having issues with my 5950X crashing on idle and low threaded tasks, but working fine on stressful high core count tasks. It'd always show WHEA Cache Hierarchy errors in the event viewer. I figured it was low voltages so I 'lowered' the negative offsets in the core optimiser but still had issues with crashing. I also tried a positive offset on the core being show in the error logs but it still crashed. I then tried RAM settings with no change. I tried raising the SOC voltage but no change. I tried changing the LLC settings on both the VCore and the SOC voltage with no changes. I made sure my power profile was set to balanced.
I confirmed that the issue didn't occur when setting my BIOS back to stock settings so I knew it was more likely to be a bios issue. HWInfo64 was showing the occasional dips in Voltage to 0.2V on some cores which further validated my theory.
Whilst it's only been 3 days, I disabled Global C-State Control and have since had no issues. Sure idle voltage is a bit higher, sitting at around 1V most of the time rather than 0.9 but that's a small price to pay for stability and confidence that my CPU isn't faulty.
My motherboard is the AsRock AQUA.