hi, here from Spain. That happens to me for long time ago. I've restored individual albums where I've detected that random songs have disappeared. It's frustrating. You have to rip again and again that albums!!!
That's the biggest problem Apple has in his history and it doesn't matter!! Programmers of Apple, please change the behaviour of iTunes, invent another type of database or whatever else, but this is UNACCEPTABLE!!!
I'm not sure that this will continue to happen if you subscribe to iTunes match, but certainly, I'm losing my faith... Apple, do something!! we've payed a lot for your iphones, ipads, ipods and macs... how can you live with that problem? do something! ðŸ˜