A very weird thing is happening with my RX 480 8GB. Overclocking memory gives me this:
Setting DAG epoch #201 for GPU0
Create GPU buffer for GPU0
And then reporting continuously 0.000 Mh/s. Any alteration to -mclock other than the value 2000, which is what the default clock is set to, will cause 0.000 Mh/s.
I have 5 other RX 580 cards running just fine on the same rig. Ample amount of virtual memory. I don't use any software. I use Claymore to apply overclocks. When I set the memory to 2000 it runs at 29.6 Mh/s without problem which fine but it has samsung memory and I'd like to try see what it can do. BIOS is unchanged except for memory straps.
Graphics cards of the same type may have all the same specs but they are slightly different (the silicon lottery) and it could be that this errant cad has reached its limits. Have a look at the memory errors with 'HWinfo' and see what errors you get as you increase the clock speed.