Running the 5.3.5 Kernel, 19.2.0 Mesa and latest firmware in Arch's repository
I am also running into the same issue:

[46623.025576] [drm:amdgpu_job_timedout [amdgpu]] *ERROR* ring sdma1 timeout,
signaled seq=75019, emitted seq=75022
[46623.025668] [drm:amdgpu_job_timedout [amdgpu]] *ERROR* Process information:
process chromium pid 24183 thread chromium:cs0 pid 24244

This happened while switching tabs in Chromium. The umr command is not
available for me, and AFAIK the official arch repository doesn't have any
packages that provide it.