My first thought is that if something stops on 2 separate devices then far from being "blah, blah" checking the account settings is the obvious place to start: account settings will be common to all devices using the same account (unlike app settings, which apply to the app on a particular device). Your post doesn't make clear whether you have actually done this or not, but uninstalling and reinstalling would do nothing if this is where the problem lies.
To be honest I'd check the app settings and device settings anyway: check that notifications are enabled in the app and check that the system isn't blocking notifications from the app (the two different ways notifications could get turned off). Sure it would be odd for these things to change on both devices, but it's better to spend a minute ruling these things out rather than waste more time because you assume it can't happen (as an example, if you could imagine something happening as a result of an app update then that update would be applied to both devices).
If it's not an account setting or a weird change on both devices I'm afraid the obvious answer is indeed a problem with your Facebook account (or a bug in the FB app that only manifests on a few people's devices). But let's hope not, because I don't have much confidence in them fixing things quickly.