The days these occurred were all over the map, Wed/Sat/Sun. Times all over the place too, so I can't find reason as of yet!Most of these errors (and the other one you just mentioned me in) are indicative mostly of the expected cache data not being available for some reason. Particularly the setGroupStyles and setMediaSites ones as that data comes straight from the cache.
I'm going to run my local install with file system caching for a bit to see if I can reproduce a similar issue, but it potentially is just indicative of the files not being read for some reason, or the reads taking longer than they're supposed to.
If there are any patterns to when the errors occur, such as at particularly busy times or similar then that could be quite telling.