To everyone who ran into the bug that won't let you progress past Date 3, the only solution I have found so far is wiping your device of any other versions of Duality. 

This means that if you have installed Duality in the past, you need to delete those folders. Everything. Better yet, if you have installed the new update, delete that as well, make sure there is nothing left anywhere and then install 3.1. 

If there are any of you who installed the game for the first time after the Date 4 update and still ran into this bug, please let me know in the comments. I will continue to look for solutions.