I just got 2nd hand 5700 xt and installed into rig. HiveOS recognizes it but it shows its pulling only 9 or 10W and zero hash with ethminer. No problems with other cards (gtx1060/1070s) running in same rig.
I have switched risers and even installed direct to 16x slot on mobo. Also tried running through Nicehas on windows. That works fine.