I also noticed they've started resetting the notification settings I set through the Android settings menu for Messenger. I didn't know this was supposed to be possible.
I think the developer can change the notification channel ID (which they use to group similar notifications and the user can disable a specific channel) and then you basically start with a channel without previous settings. You would have to disable all notifications for an app completely (not just a specific type) to prevent this for the future.
Thats what bothers me the most about my Samsung phone. Facebook came preinstalled and I cannot uninstall it. I can only deactivate (whatever that means).
I don't use facebook, I actually never did. Its not the fact that I'm loosing a few MBs of storage that really bothers me, it's the fact that this is the facebook app.
I don't have it on my phone and I don't see a reason for a native app for facebook. The mobile website works good enough if I need to check something (sadly it's heavily used also by companies and newspapers in my country) and messenger works through https://mbasic.facebook.com/messages/