iCloud sync not syncing

I'm getting some weird things happening on my sync between my MacBook and my iPhone.

I've created a playlist on the MacBook and synced it. The playlist has 26 songs but then when I sync my iPhone, the playlist is there but with only 24 songs. If I sync on my phone and then go back to the MacBook, my original playlist now has only 24 songs.

If I add the two songs back in (and it's the same two songs every time) and sync then exactly the same thing happens again.

THere's nothing particularly complex or unusual about the two songs and I don't know what else is going on in my playlists but just noticed this as its the one I'm working on at the moment.

I do have a lot of playlists, is there a limit after which it starts misbehaving?