What I noticed from the kern.log is that it seems to try and skip init steps
the second time amdgpu loads. So perhaps the unbind doesn't do a clean enough
shutdown or there may be a bug in the init step skipping.

For example, the first time:
> [  129.439652] amdgpu 0000:01:00.0: enabling device (0000 -> 0003)
> ...
> [  129.918128] [drm] GPU posting now...

The second time:
No mention of enabling device.
> [  159.722828] [drm] GPU post is not needed