i have the same issue was getting 60fps in overwatch and the game would start at 60 but after a sec it would drop to 20 fps and stay at that fps. i was getting the same issue in rocket league from 60 i would go to 40.
i had the lines as well i thought it was an artifact so i decided to the the record feature in re live and it went away after recording a video. go figure aye.
rolling back removed the issue so the driver needs some work.
win 10 64
If you a recordong via ReLive - try to set frequency to 48 KHz in Windows settings for sound card.
Same problem, reverting back.