Board Thread:Questions and Answers/@comment-72.71.150.182-20150426170002/@comment-26021614-20150427161328

Chances are your game resets because you are using your phone's memory elsewhere, and it cannot keep your game on when running another app. If you don't use your phone at all while you wait for your energy to recover, it will work.

If you are talking about "Unexpected error has occurred." that occurs because you tried to enter the dungeon too soon, like within a few seconds after your energy has recovered, and the game hasn't caught up to it yet, i.e. the timer was off by a few seconds in the game vs. on your screen, and so that causes the game to crash and restart.