Unfortunatley one GPU connected over a riser is freezing all the time, sometimes after 3 h, 7 h, 20 h or even 5 min.
Got similiar problem in past, i checked everything, power source, motherboard, ram, cpu everything.
Turns out, my GPU was bad physically, i mean i sent it back to producer and he fixed it.
Same thing it was, random freezes 5 min / 3 h / 5 h etc.