I'd return it if you still can and just get a 2060S, especially if you play older games. Looking at reports online, it's not much slower, it will just work and I think you can get adaptive sync working on most monitors without gsync now.

new Navi graphics architecture = driver problems with older games
new PCI-E 4.0 support = BIOS problems with older hardware

These things will get sorted out eventually but man... kinda wish I waited longer now to upgrade my PC. This direct x error will probably never go away either. Given it's history... it's a game engine issue and probably not fixable. The 5700 cards just happen to trigger it more often...