Seems to not be hardware related. Strange black areas depending on view direction. HDRI environment (visible in video) No other lights etc.
Ok, after a lengthy process of elimination with HDR etc the problem is identified - user error.
More specifically in the bump area of the node tree, Factor output from the Noise Texture Node was plugged into BOTH the Height and the Normal input of the Bump node. Removing it from Normal and leaving only Height input connected solved the problem.