It seems that a recent update changed the navigation, such that when you are reading a message and delete it, the app goes on to the next message rather than going back to the email list.
Yes it seems that the latest V10.2.1465 now “doesn’t go back to the Inbox after opening and reading an email”, which I suspect is a bug rather than a change in the app.
There was also another user @rsaeks who also found that same thing now happening (and also myself in the latest Droid app) in the thread below. So hopefully the next mobile app update will have either a fix for that “or if it’s not a bug” then an “app setting to go back to the Inbox” like before.