Release 5.5 simply doesn't work for me. Any song that's already cached won't play - songs that are streaming directly are playing ok. If I have a play list where some of the songs are preloaded, I can skip to any song that's not marked yet and it will play, go back to any that are already on the device and it just sits there. After a short while all my songs are on the device and none of them play any more.
I went back to 5.4 and everything works fine. Upgraded to 5.5 and again it's all broken. Apparently a new bug was introduced.