I use to get the same idle reboots and WHEA errors in the event viewer with my setup as well. After going through forums, I found after setting the following, I stopped getting these issues.
After performing a load default settings, go back into BIOS and set these entries:
AI Overclock Tuner: D.O.C.P Standard
Memory Frequency: DDR4-3600MHz (set it to whatever your RAM advertises)
FCLK Frequency: 1800MHz
DRAM CAS# Latency: 16 (this should be set by the DOCP Standard)
Trcdrd: 16 (this should be set by the DOCP Standard)
Trcdwr: 16 (this should be set by the DOCP Standard)
DRAM RAS# Pre Time: 16 (this should be set by the DOCP Standard)
DRAM RAS# ACT Time: 36 (this should be set by the DOCP Standard)
Trc: 52 (set it to whatever your RAM advertises)
SB Clock Spread Spectrum: Disabled (this will get your Bus Clock to show up as 100MHz instead of 99.8MHz in HWInfo)
DRAM Voltage: 1.35 (this should be set by the DOCP Standard)
1.00V SB Voltage: 1.00 (explicitly set this to 1.00)
1.8V PLL Voltage: 1.80 (explicitly set this to 1.80)
SVM Mode: Enabled (so that I can run VMs)
Global C-state Control: Enabled
Power Supply Idle Control: Low Current Idle
DF Cstates: Enabled
CPPC: Enabled
CPPC Preferred Cores: Enabled
Aside from these settings, I turned off all Q-Fan Controls and turned off Fast Boot. Not sure if they make a difference, but I haven't ran into any more idle reboots or WHEA-Logger Processor Core errors.
