and in iTunes, check the playlist that is on the iPod.

If you manually sync only selected playlists, remove the new playlist from the selection and re-sync.
This will remove the playlist from the iPod. Check that it did.

Now make sure that everything in the Playlist is actually playable.
If all is well, add the Playlist back into the sync selections and re-sync.
Check the iPod for the number of tracks in that playlist