Since the latest Android update (1.20) the back button doesn't always work. For example: tap through from the home page to stats then books read then to an individual book's page and then tap the back button will take me back to the stats page but not to the home page. Previously the back button would work just like a web browser back button and go back to the previous "page". Now sometimes it does and sometimes it doesn't.

Phone info: Samsung J7 on Android 9