Per Linux Kernel 5.0 release here an updated report with that newest kernel and
updated head from git://anongit.freedesktop.org/mesa/drm

With the Linux Kernel 5.0 the dmesg log if full of amdgpu spam, that seems to
repeat itself all the time, independent of operation - not sure if it's related
to the grub debug line.

The the freeze though seems to still appear the same way but the error message
in dmesg has changed and now just shows two lines: that occur at the freeze
point:

[ 2501.329358] [drm:amdgpu_job_timedout [amdgpu]] *ERROR* ring gfx timeout,
signaled seq=300047, emitted seq=300049
[ 2501.329419] [drm:amdgpu_job_timedout [amdgpu]] *ERROR* Process information:
process ShadowOfMordor pid 3150 thread ShadowOfMo:cs0 pid 3152
[ 2501.329421] [drm] GPU recovery disabled.

Full dmesg log and glxinfo output in the new attached
dumps_from_dmesg_and_glxinfo_2