Maybe your MC library is corrupt. You could try re-importing.
Before I tried using MJ on this library I did create a new library and imported all my files fresh. I still had the lag.
When I installed MJ12 I restored a backup of this library from Media Center into Media Jukebox, so essentially they both are using the same library. MJ is not showing the lag.
This seemed to begin when I converted a copy of my Flac files into MP3 and added them to the library, making it quite large. But if I had hit a size limit "wall" then I'd expect MJ to react the same.
?
One odditity I repeatedly see is at the end of an Import, "Analyzing Linrary 39537 files"
The library is much larger than that, and that number does not correlate to anything I can recognize (such as new imports). I have been seing this for some time, only a while back the number was 12,871 files.
Could this be some "junk" in the database that needs cleaning? Broken or left-over links?