This is an old post I know...
I have this problem with the pegged core with my secondary GPU, a radeon r7 360. The funny thing is I always have that problem in 6.10 and later. So I stuck on 6.9. But I recently noticed that I actually sometimes have it on 6.9 as well. The sporadic nature, and the fact it seems to never happen on first boot, but once it does happen one VM that uses it might book OK but made me thing it is some kind of resource leak or something. Can you explain the 'memory not mapped properly' issue I might encounter and how I would troubleshoot it? I have plenty of free memory but I could see some sort of fragmentation issue being involved. I'm pretty stumped on this one though.