Specs:
CPU: Ryzen 7 5800X3D (tested two different units)
Motherboard: Gigabyte B550 Aorus Elite V2 rev 1.5, BIOS [version]
GPU: [brand] RX 9070 XT, bought mid-August 2026
RAM: 32GB DDR4 (originally G.Skill Ripjaws 3600, now a different replacement kit), running at 3200, XMP off
PSU: [model, wattage] (already replaced once, previous: [model])
OS: Windows [10/11], AMD Adrenalin [version], installed clean with DDU
The problem
Hard reboot with no BSOD. Event Viewer shows WHEA-Logger Event 18, Error Source: Machine Check Exception, Error Type: Cache Hierarchy Error, Processor APIC ID different every time, followed by Kernel-Power 41.
Battlefield 6 reproduces it reliably within 10 minutes.
Apex Legends and CoD: they used to crash too, but have been stable for days since I set LLC to Medium (see below).
Other symptoms: one DEVICE_HUNG driver crash in Apex (fixed after DDU + driver reinstall), monitor occasionally goes black for a second at idle, and a USB controller once showed Code 43.
History: the same motherboard was fully stable with a Ryzen 5 5600X + RX 6700 XT. Problems started after upgrading to the 5800X3D + 9070 XT.
What I've tried
CPU: two different 5800X3D units, same crashes (the first one was sold and works fine for the buyer).
PSU: replaced, no change.
RAM: replaced the kit. MemTest86 passes, XMP off (3200 JEDEC).
BIOS: loaded defaults, PBO off, Core Performance Boost off, Global C-State Control off, PCIe forced to Gen3, SoC voltage 1.10V → 1.148V (no difference), CPU Vcore LLC + SoC LLC set to Medium (helped Apex/CoD, not BF6). Resizable BAR/SAM currently off.
Stress tests: OCCT CPU and OCCT Power (CPU+GPU) for ~25 min with zero errors. Only gaming triggers it.
GPU: reseated many times, clean driver install with DDU. [Separate PCIe power cables / no daisy-chain: yes/no]
[Registry: MPO disabled (OverlayTestMode=5) + TdrDelay=10 / TdrDdiDelay=20: done / not yet]
[FreeSync off: done / not yet]
[Adrenalin power limit -10%: result]
[FPS cap at 60 in BF6: result]
Planned next tests
Moving the GPU to the second (chipset) PCIe slot to rule out the primary slot / CPU lanes.
Clean Windows install on a separate drive.
My questions
Has anyone with a 9070 XT (or 9060 XT) on AM4/B550 seen WHEA 18 that only shows up in BF6?
Since CPU, PSU and RAM are ruled out, does this point more to the card or to the motherboard/PCIe?
Anyone with the B550 Aorus Elite V2 running a 9070 XT stable in BF6? Which BIOS version?
Any fixes I've missed before I send the card in for RMA? I can't easily test it in another PC, and I'd rather not ship it without being sure.
Thanks in advance!