If nobody has given you an answer, the odds are good nobody KNOWS the answer. Bumping your posts and saying "please" will not miraculously give us the answer.
The fact is that if there seems to be no pattern to it, there isn't much we can diagnose. All we can give you is the basic steps:
-Reformat the iPod and restore all of the software
-If that doesn't work, take it to an Apple Store or some such location.