Android app crashing on start

I have been using the android weekplan app multiple times a day without trouble. However, since this morning the app does not even start. I get right to the "Week Plan has been closed repeatedly" pop up. Closing the app, clearing the cache and data as well as uninstalling and reinstalling did not help either.

I am really a heavy week plan user, so getting help on this one is absolutely urgent to me.

Many thanks in advance!