Also, every time I've tried to use Afterburner with a 7-GPU rig, the whole thing crashed after it applied OC's to the 7th card. There must be some limitation there.
Seems we are on the same boat. Why the 7th card has to be a problem?. I ended up NOT using Afterburner at all. Yes there must be an issue there with AB and the RX5xx drivers. At this moment I set all OC and Undervolt on Claymore even though sometimes cards do not take it right away. Known issue of Claymore.