I had the EXACT same problem as you with my XFX RX 6800 XT Triple-Dissipation model (what a mouthful). Initially, it was fine for a bit and then it started crashing badly. We're talking green-screen, buzzing sound and full system reset. It was even doing this in older games like Bioshock Infinite and Dragon Age: Inquisition.I also said the 2x times the cost of the 5700 xt for a card that would crash is not worth it. The driver read me list that as a issue and black screen sometimes.
Nope it could be the card. its done it since day one, The one in the system for 60 days before the 5700 xt was a AMD card (R9 390X) and it worked fine.
The 5700 XT run fast it just crashes. it only crashed one time tonight.