In the latest Android app, the back button in the forums isn't working right. When I'm reading a message and want to go backwards, pressing the back button returns to the home screen of the app instead of to the previous screen. This is definitely some new behavior with the latest version.
This is unfortunately due to an issue in Chrome for android 63+. It looks to be fixed in version 65, but that version is still in beta. Updating to Chrome 65 when it is released will resolve the problem, but in the mean time, using a web browser instead of the app will give a better experience.