i'm not sure if this will help you but the same thing kinda happened to me. it just didn't show my friend list anymore. what i did was go back to an earlier easier level (easier to win) and played it, at the end of the level, it'll show the friend's list again at the bottom.
It says to complete levels to climb the list. I’m currently #17 but I have no more levels to play until next Wednesday when more are released. Is that the only way to climb the list?