Some additional information I had neglected to mention in the initial
description in the "excitement" of filing my first bug here...

Relevant hardware is as stated a ryzen 2200G running solely on integrated vega
graphics - I haven't mentioned any other specs of the system as this bug has
persisted across replacements of all components, even the motherboard - only
things that have not changed are the PSU, nvme storage and the ryzen chip
itself.

Distro is arch linux with all packages up to date at the time of writing.
Kernel version 5.2.1-arch1-1-ARCH. Mesa built-from-git version mentonied in bug
description. LLVM version 8.0.1.

Any other information is available on request.