Screen flickering/turning off

[thelordsmith]

Hi All First time poster here. 
I'm after some help as im stuck for ideas now. I have x2 pc's that have the same problem spec is below. 
When the GPU is in the riser cable im getting the screens flickering and turning off and on again. When the GUP is plugged in to the Motherboard directly the fault disappears. This would point to the riser cable being the problem so i started changing BIOS setting ie setting the PCIE slot to gen 3 then gen 2 and still get the problem. next i had the cable replaced by phanteks and still get the problem, iv tried looking for voltage settings to turn up the PCIE voltage thinking it might be voltage drop over the riser but i can not find any setting for that. 
Anyone else had this problem or similar problem and found a fix to it. 
They are pc's in a office environment but the client wanted a more posh looking case as they are on reception 
Arous B550I AX
Ryzen 5600g
Corsair LPX ram 16gb

Corsair 650w SFX psu

Phanteks Evolv Shift 2

Thanks all.