Hi,
I'm having this problem with my pg248q monitor only when G-SYNC is active. While playing any game (LoL, GTA5, BDO), I will get these big horizontal black lines on my screen, consistently. I tried installing the newest/older drivers, different refresh rates and changed display port cables (using the one that came with it). My graphics card is at factory settings, I've tried recording it but it doesn't show when you watch it. Monitor was fine until 2 days ago. I'll attach some pictures of it.
Specs:
Windows 7 64bit
i7 6700k
Asus Strix GTX 1080 ti