Very happy to report that 26.4.1 seems to have resolved the issue for me. No code changes needed. I just updated and notification are working as expected. Thanks a lot, Ziqiao!

Thank you for spending time with me on this. I had forgotten to update my iPad to 26.4 and it's still running 26.3.1a, which had about 60 push notifications received from my testing along the way, haha. I've tested every single notification group I have and they all work perfectly fine on 26.3, but not on 26.4 on the same app build. I've submitted detailed feedback: FB22343785

Have added another reply to the thread with more details, it didn't fit as a comment...