I don't remember the quest name, but I stepped on one that was too high level at the time and chose the option to come back later.  After that, every turn, regardless of where that unit stack was, it would pop up the menu of undergoing the quest's fight or coming back later.  i restarted and reload but bug was still there.  So I clicked for the fight I knew would squarsh me just to see if it would simply go away, and the Guardian Statues kicked my ass.

This is only the second time a bug has forced me to start over in FE.  Not too bad, really.