It looks like bad GPU. But first look at your GPU temperature when the card is in mining mod. Maybe the problem is overheating. Or it can be the faulty GPU memory.
 
You tried to:
1. Change risers.
2. Change PSU.
3. Put GPU in PCI-e x16 slot.
 
Conclusion:
Install clean windows and put only that faulty GPU without raiser to another PCI-e slot that works.
If the card stops the same way then the card should be returned definitely.