I have the same issue - I am running ArchLabs with arch repos, recent drivers,
lutris installer of Overwatch. When firing D.Vas rockets or certain other
sparkly effects, the gpu hangs. This is dmesg of when it happens:
https://pastebin.com/VBtc5nxE

My specs are

CPU: A8 2.3ghz quadcore

RAM: 8GB

Video: Radeon R5 M240 with 1gb "dedicated VRAM" AKA southern island "Mullins"
GCN1.0

I am currently using the radeon driver, which works fine (actually very well -
I have vdpau and most other relevant packages installed, and glxinfo tells me I
have OpenGL core profile 4.5 working). I cant get amdgpu or vulkan to work
sadly, so this issue makes overwatch unplayable. I use the stock ARCH kernel
4.18