Okay, after a bit more fiddling, it appears it’s an access violation:
Exception thrown at 0x00007FFAC80AC748 (UE4Editor-D3D11RHI.dll) in UE4Editor.exe: 0xC0000005: Access violation reading location 0x00000000000000C0.
It happens with SetGraphicsPipelineState(RHICmdList, GraphicsPSOInit)