Can you see what you have in common?
Third party plug-ins?
Any crashes during updates?
King's lyrics finder and Rhino's PlayingNow are the only third-party plug-ins I use, apart from DFX which I don't know if it can be considered a third party plug-in. Rhino's and DFX are always on, while King's is only used once or twice a week.
The ony "special" thing I can remember is that, as I explained in the other thread, MC froze while downloading some lyrics with King's plug-in and I had to kill MC via Task Manager. That event happened the night before, though, and I can't tell for sure if the name of the songs was missing when I first started MC the next day... in fact, I discovered the problem a couple of hours later and not at the beginning of the session.
Anyway, not all the files that had the name missing were in Playing Now for getting lyrics, that's for sure, nor were they in the same HDD.