This is actually an older issue, the game's dx12 mode got updated with some kind of caching mechanic in spring, but it's crashing on AMD since then.
My R9 390X is randomly crashing in-game and my friend's R9 Fury X can't even pass the initial caching screen, instant crash before the progress bar fills.
Have you tried the new 18.9.1? This title runs well for me on my RX 580 and has since the game launched. There have been a couple drivers that messed with free sync and seemed to stutter at times. This latest driver is flawless for me. I realize it may be different on your R9 but this may be a model issue not an AMD issue as it works great for me on my RX 580. I will try it on my R9 380X and see if it is an issue there and report back if it is. If you have not done a clean install of your driver in a while that may help.