(In reply to Andy Furniss from comment #5)
> (In reply to Christian König from comment #4)
> > (In reply to Andy Furniss from comment #3)
> > > It seems that I can make it work reliably by setting my cpus to perf with
> > > cpufreq.
> > 
> > Sounds like some kind of race condition to me, e.g. something isn't properly
> > protected and multi thread save.
> > 
> > That's probably pretty hard to find.
> 
> Turns out I can also provoke this with kodi if I try enough, and cpufreq
> perf doesn't always help mpv (but usually does).

Please try the following: Start mpv with gdb, set a break point on _mesa_error
and get me a backtrace where this error message is coming from.

Going to be on IRC for the next hour or so for questions.