iTunes wont play my whole playlists.

My problem is really simple, yet very annoying, I have a playlist composed of 33 songs, but iTunes will only play 20 random songs, another playlist of 25 songs will just play 22, I dont know what's happening and if there's a solution, or if I will need to reinstall it.

Thanks for your answers.

EDIT: The problem is partially fixed when you select the whole playlist and right-click any song, then play next. But there is still a problem with iTunes.