Under Construction message when opening Friends on iPhone

A week or so ago when I would open my game on my iPhone, I started getting a screen showing an "Under Construction" sign at the end of a level - and telling me to play earlier levels (see attached). I thought maybe I needed to install an update, but when I go to the app store there is no update available. Sometimes when I click Open from the app store, it takes me to my level. Other times, if I close the Friends app completely and then reopen it or go away for a while or play the level on my iPad and come back to the iPhone later then it opens normally at my next level.

What's going on? I'm currently at level 1669; the construction is always at 1560. Thanks for any help!