Since upgrading from Expo SDK 45 to 48 (and therefore migrating from the firebase js sdk to the official react-native package), notifications on Android are not working anymore (tested with the online notification tool as well).
Nothing was changed in the corresponding google & firebase accounts or the google-services.json file.
simply uninstalling the messaging package from react-native-firebase solved the issue (even though I was not using it) There seems to be some internal clash between it and the expo-notification module