Check your displayport cable, if pin20 is active it's faulty and not using the standard which can cause the problems you guys are experiencing.
More info here:
https://hardforum.com/threads/displayport-cables-must-not-use-pin-20-warning.1803684/ (English)
http://www.sweclockers.com/forum/trad/1453075-varning-for-vissa-displayport-kablar-kan-skada-gpu?p=1 (Swedish)