I’ve spent some time debugging this today and observed the problem you indicated.
I suspect the thing comes down to the fact that OpenGL stack shipped by AMDGPU-PRO is not available inside the snap mount namespace and the proprietary amdgpu kernel driver is incompatible with Mesa.
We have some workarounds to deal with identical problem in NVIDIA proprietary stack. There is some work on improving OpenGL story of snaps scheduled already, so hopefully will have a proper solution rather than an ugly nvidia-like hack. I’ve poked at different things and collected some data in the process. The userspace bits seem a bit lacking compared to what NVIDIA ships (eg, lack of glvnd), though it’s unclear if that will affect us.