This is a tricky one and the answer comes courtesy of robburrito at

He suggests logging on someone else’s device. To do this, they have to close out the app from their home screen (double tap home button, hold then close app), then will be prompted at the “welcome back” screen to tap to continue. Have them (or you on your other ios device you’ve downloaded the app onto) hit the origin icon, then logout. From there you should be able to log back in as your town and it should open up.

He says that once most characters are tasked and income collected from buildings, the app will open on your original device.

You can see what he says at:

You could also try this: go to from your pc or laptop and login there. Then go back to your phone or iPad and try again.