That was happening to me with GWX (but not with NYGM). I'm convinced it's artifacting due to an overheating CPU/graphics card. I turned down my core voltage from 1.6v to 1.5 (not sure why it was at 1.6...) and the problem went away immediately. On a really hot day I get the occasional crash, and some artifacting. I think GWX just drives the system harder.
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