@Adam Hey there - I (Monica) don't have an Android device to check this, but this recent post on the K-9 Mail forum might be helpful for troubleshooting this: https://forum.k9mail.app/t/cannot-get-push-notifications-to-work-on-my-inbox-folder/8837/7

Also, we're using all the feedback to help us create FAQs and Getting Started guides on Mozilla Support, and I've added a note we should include Push and Poll settings in said guides.