Hi,
I have an issue of not receiving Facebook messenger messages unless connected to WiFi. Permission for mobile data is on, emails, whatsapp, facebook etc all receive as they should but the fb messenger app will not.
Any help on settings would be welcome.
Thanks.

Hi friend, if all the others are ok, then your issue will be strange.
Can you please check again? If you have done some setting on the facebook message.

Do you experience the problem when the Messenger is onscreen, or only when is expected to work in the background? If the latter, did you add the Messenger to the white list to prevent closing it by the energy conservation mechanism?