Fb Messenger background refresh not working

The problem is not receiving push notifications from Messenger, I get those just fine; on lock screen, notification centre and the badge app icon. When I then open Messenger, all the notifications clear away immediately as they should.

The problem is when I get a notification on my phone, sometimes I open Fb on my laptop to respond to the message(s), then the notifications won't clear from my phone. They remain in the notification center and the badge app icon stays too, as if I haven't already seen all incoming messages, no matter how I long wait. The only way to make them disappear is to open Messenger so that it can refresh, on foreground basically.

I've tried reinstalling both Messenger and the Fb app, logging out and in again, restarting my phone. All settings are set as they were when everything was working properly (push notifications and background app refresh is on etc.).

Any help would be appreciated, thanks.