We're sorry to hear about this. Have you tried switching the Renderer to Mercury Playback Engine Software Only & checked if it's working properly? Also, is this happening with any specific media type or is it with all the media files?
Yes I have switched to CPU rendering which solves the blacked out window issue, but the footage playback is much choppier even at its lowest quality settings. This is currently happening with 5k Red footage but it happens all the time with footage from varying sources.