I had exact same issue with 5900X and found I had to set +5 all core on curve to prevent BSOD while idle. I've since raised RMA with AMD.
95% of the time the WHEA errors pointed to APIC 8 (5th Core), which is actually what Ryzen master designated as my best core. Even at +5 it would still crash. With HWInfo reporting that sometimes the voltage would drop to 0.2V at idle I wouldn't think that's a CPU issue as such, more of a power delivery one.
I'm happy enough with turning off Global C-States for now at least.