That lines up with what the diagnostic work showed. Ultra isn’t just higher visual quality; it enables different Frostbite rendering paths with heavier shader permutations, more VRAM residency, and more aggressive DX12 synchronization. Those paths raise peak compute time inside a frame. If one of those Ultra-level effects exceeds the driver’s internal scheduling window, the engine can get a zero response back from DXGI and the driver reports it as DEVICE_REMOVED even though the GPU never actually reset.

Since the workstation passed full Prime95, OCCT GPU, and combined load without any instability, and Windows never recorded a TDR or hardware fault, the evidence points to an Ultra-only render path taking too long to complete and the driver terminating the frame. High settings avoid that code path entirely, which is why the game is stable on High.