I'm using RX 480 and experiencing same kind of problems. Running Unigine
Superposition crashes GPU 4 times out of 5. I can reproduce these crashes also
by playing Euro Truck Simulator 2 but then it's directly dependent how high I
set resolution scale in game settings. Larger scale causes crashes to occur
more often. When booting my machine to Win10 (I'm running dual boot) everything
works fine. 

System info:

CPU: Intel i7-3770K
GPU: AMD RX480
Arch Linux
Linux: 4.17.14
Mesa: 18.1.6
LLVM: 6.0.1