Just for the record: To rule out my personally compiled kernels are somehow
"more buggy than what others compile", I tried the current Arch-Linux-supplied
Linux 4.17.2-1-ARCH kernel.

Survives about 5 minutes of Firefox-browsing between crashes with:

Jun 20 00:01:11 ryzen kernel: [drm:amdgpu_job_timedout [amdgpu]] *ERROR* ring
sdma0 timeout, last signaled seq=1895, last em>
Jun 20 00:01:11 ryzen kernel: [drm] IP block:gmc_v8_0 is hung!

(4.13.* did at least survive days.)