How to prevent iOS 10 apps from "resetting" when activated after being backgrounded?
This is due to the restrictions iOS places on app developers.

Apps are only allowed to stay open in the background for a few minutes (this saves RAM), so if the developer doesn't have the app save where you were last, the app will reset to its start page. So no, you can't do anything about this.

This is why you don't really need to close your apps in the app switcher.