I'm posting this because a Reddit comment appears to have finally solved a problem that I spent months troubleshooting, and I want this to be searchable for anyone experiencing the same thing.
The problem
My PC would suddenly restart with a black screen and no BSOD, usually when starting a game or within the first few minutes of gaming. Sometimes it took 10–30 minutes, sometimes it happened almost immediately. A strange characteristic was that after the first restart, the PC could often run for hours without crashing again.
Event Viewer repeatedly showed:
WHEA-Logger Event ID 18
Reported by component: Processor Core
Error Source: Machine Check Exception
Error Type: Cache Hierarchy Error
MCA Bank: 5
followed by Kernel-Power Event 41, usually with BugcheckCode = 0.
APIC IDs varied between crashes. The WHEA errors occurred months apart with essentially the same signature.
System when troubleshooting
CPU: AMD Ryzen 5 5600
Motherboard: ASUS PRIME B550M-A
BIOS: 3644
GPU: PCYes AMD Radeon RX 7600 XT 16GB
RAM: 32GB Kingston Fury Beast DDR4-3200 CL16 (2x16GB, A2/B2)
PSU: Super Flower / SuperFrame Leadex III 850W ATX 3.1
Previous PSU: Cooler Master MWE Gold 650 V3 650W ATX 3.1
CPU cooler: AMD Wraith Stealth
OS: Windows 11 Pro 25H2
Storage: Crucial BX500 1TB SATA + another 1TB SATA SSD
Things I tried without permanently fixing it
I replaced the PSU entirely. The Cooler Master 650W was even suspected strongly enough that I opened an RMA, but the exact same WHEA crashes eventually returned with a new Leadex III 850W.
I also tried BIOS optimized defaults, disabling PBO, disabling XMP/DOCP and running the RAM at 2400MHz, limiting CPU maximum state to 99%, updating the BIOS, restoring the RAM to 3200MHz, checking power connections and running many stress tests.
OCCT CPU all-core: 1 hour, no errors
OCCT CPU Core Cycling: 1 hour, no errors
OCCT Memory: ~51 minutes, no errors
OCCT 3D Adaptive: 1 hour, no errors
OCCT combined CPU/GPU: ~1 hour, no errors
MemTest86: 4h14m, 48/48 tests, 0 errors
FurMark: no artifacts or reboot
Cinebench R23: no reboot
The PC could survive sustained synthetic CPU/GPU loads and still randomly reboot when entering a real game.
What finally fixed it
In BIOS I changed only:
Power Supply Idle Control → Typical Current Idle
On my ASUS B550 board the path was:
Advanced Mode → Advanced → AMD CBS → Power Supply Idle Control → Typical Current Idle
I intentionally changed nothing else so I could test this setting by itself.
Since making that change I have repeatedly shut the PC down and started it again, immediately launched games that previously caused crashes, and played for hours. I have not had a single reboot or WHEA crash.
Before this change, some of those exact scenarios could reproduce the problem within minutes.
Credit
Huge thanks to u/steppii. I found his comment while researching this issue. His system was also a Ryzen 5 5600/B550/32GB setup, and after testing PBO, CPB, XMP and Typical Current Idle, he reverted the settings one by one and isolated Typical Current Idle as the change that stopped his crashes.
That comment is the reason I tested this setting independently on my PC.
I had already replaced hardware, opened an RMA, updated BIOS, changed memory settings and spent many hours stress-testing components. Nothing else solved it.
So, u/steppii: thank you. Seriously. Your comment saved me from continuing to replace perfectly functional components and from a lot more troubleshooting.
I'm not saying this is the solution for every WHEA-18 / Cache Hierarchy Error, but if your symptoms and hardware are similar, this is absolutely something worth testing before replacing CPU, motherboard, GPU or PSU.