I honest to god had the exact same problem sometimes, and I too, have an RX-480.
I had the problem for about a month and it happened randomly, but updating drivers on everything made it go away eventually.
It seemed to happen when swapping windows too fast, sometimes even games would make it freak out.
I had the same exact thing and sought help, but just waiting it out was the only solution. Even a fresh OS made it do it. #HauntedHardware?
Hopefully it fixes itself for you, too.