I also have the problem described in the forum here by many others and am frustrated that Apple hasn't acknowledged the issue or provided some sort of endorsed solution. My Itunes reports that I still have 30GB of music stored on my iPad, yet all music playlists, titles etcetera are Blank with 0:00 song length and can't play anything. Odd think is that when hooked up to iTunes, I can see the list of the music that is physically on the iPad and play it from there.
Many different solutions have been offered in this thread, but would like to see a recommended solution from Apple rather than simply go through trial and error for all of the suggested ones here beyond the standard 'turn off/on iMatch' which doesn't seem to have any results.
Please help all of us frustrated people Apple, this is ridiculous (Not to mention the different problem I had on my iPhone where iOS6 deleted all my music natively stored on my phone and made me download it again from the cloud instead of remembering which was previously on the phone and in the cloud).
What a nightmare iOS6 is for users who also use iMatch and have paid extra for this service.
CC