I was also impacted by this bug (amdgpu hangs on random conditions with similar
messages as the one exposed) with any kernel/mesa version combination other
than the ones on Debian Stretch (any other distro or using Mesa from backports
would trigger those crashes).
This was on a Ryzen 1700 platform with chipset B450. I had this issue with a
RX480 and a RX560 (as I tried to replace the GPU in case it was faulty, I also
replace the motherboard).

I was still impacted with Fedora 30 with recurring GPU hangs. Then I replaced
the CPU/motherboard with a Core i7-9700k/Z390 platform. Since then I did not
have a single GPU hang on Fedora 30.

My hypothesis on this problem not being easily reproducible is that it would
happen only on specific GPU/CPU combinations.