2nd GPU / riser problem - Windows boot freeze

Hi! I'm having a hard time connecting second GPU (2x3080) over the 1x to 16x riser (PCIE3 slot) to my B550m Pro4. After connecting second GPU I can boot to Windows normally, but the 3080 shows as Microsoft Generic Display Adapter. After Windows installs the drivers for the graphics card the system becomes reeeaaaly laggy (few seconds lag) and the device state is "Windows is uninstalling drivers" (code 21 AFAIR). When I connect the riser to PCIE1 - no problemo alles bueno. From what I have read this board is supposed to support dual GPU (8x/8x PCIe config, but still). I'm currently waiting for a PCIe splitter like suggested here .

System: 3080 v1, 3080 v2, 5600x, B550m Pro-4, Seasonic PX-850 W, Windows 10 Pro, 32 GB DDR4


I have already:
- disabled CSM and reinstalled Windows
- changed PCIe GFX lanes from 16x to 8x/8x
- changed PCIe speed from Auto to Gen2 and Gen1
- enabled 4G decoding
- disabled resizable BAR
- try to install drivers with only over-the-riser GPU installed - same result
- creating 32 GB of paging file

Anyone has any luck with such system configuration?

Hello, im having the same issues on my b550m motherboard with ryzen 5 5600g

So where did you connect your pcie splitter? To the x16 slot or x1?

Thanks in advance