Seems that the treasure mill bonus hasnt been working for over 6 months according to other posts.

eleblanc01

I too have this issue and it crashes each time I try to play...what are you doing to fix this problem.  Doesnt sound like there is much effort going in to fixing this problem!  Not too impressed with your replies to other people's post since this has been going on for too long

KingsPinn

The last posts about this said to make sure that you have the latest update of the game. Check your app store, make sure you're up to date and it should work fine. It did for me