Try using DDU > download ddu and do a clean uninstall of the graphics drivers. I just had the same issue with my R9 Fury and this is the only thing that worked. Make sure disable auto start of any of the other graphics card OC software (TRIXX, Afterburner etc.) first before the uninstall using driver uninstall or for the clean install of the new drivers.
There were a couple of wattman changes which now require all 3rd party oc apps to be modified/updated. May even apply to clock blocker ?
Uninstall them, if you stay on new driver.
If you then still have the probs, use the "Report Issues".
I have a 390, W10 (no gtav, but other games running fine).