I had nearly the identical system running not too long ago, so I might be able to help.
I would also suggest that you monitor the GPU temperature, as the card will shut itself down if it gets too hot in order to prevent damaging the card. This can be controlled and monitored through Radeon Settings.
Do you have another graphics card to try temporarily? Doesn't have to be anything too serious, just for troubleshooting purposes. Is this a reference design card or the Gaming X series card with the dual fans? The adapter itself could likely be the culprit if none of the drivers are fixing the issue. What sort of tests were run on the graphics card when you brought it in?
Thanks for weighing in. I'll take a look at the Radeon Settings to see if the card is overheating.
I have an old card in now, a sapphire HD 7770 and, for an older card, it seems to be working fine running off of what appears to be the same driver as the RX480. No freezing, no black or blue screens. A little choppy with some gaming, but nothing out of the ordinary.
The MSI RX480 I have is the Gaming X series.
I don't know exactly which tests were run by the shop as I left the card with them. I know a stress test for sure, and I believe they also removed it from my system and took it for a spin on their in-house testing rig. Beyond that I cannot say.