Could you try that option I mentioned? If a software button fixes it (because that way it doesn't matter whether the OS is failing to direct your back button press correctly) that should be easy for us to add for everyone.
More generally: we give away Screen Reader for free and we give away Screen OCR for free with our OCR add-on (which we have to pay to license, so we can't give that away for free) precisely because we don't want people to be stuck paying for something that doesn't work reliably. Screen Reader exists in a sort of no-man's-land where Google hasn't technically banned anything we do, but they strongly discourage it, don't test that it works correctly on new devices, don't document most of it, and don't even offer APIs for some seemingly obvious things like "what exactly are the usable boundaries of the screen for me right now." So we're doing the best we can but frankly it's kind of a miracle this feature works at all
(but if you're disappointed with your purchase we're of course happy to refund anything you bought within Google's 1-year return window)