Run android app in background

So my game is pretty much finished, all published through the play store etc. But I just noticed an issue that when you minimize the app (exit out of the application and go on another app) and then try and switch back, it just crashes and the app will restart. Is there something I am missing to make it not do this ?? I noticed that app switching works fine on the unreal match 3 demo project, but I could not figure out what they had done differently to make it work.

Cheers!