Wifi Calling intermittent - any ideas why?

[jrgloucester]

I have Wifi calling enabled on my account and on the phone.

The issue is that sometimes it works, at other times it does'nt. I'm trying to use it from home (where reception is terrible). Nothing else changes, my wifi and internet access is fine (high speed broadband), nothing changes on the phone (Samsung A40), but sometimes it is there, other times not.

Any ideas ?  Very frustrating as I upgraded to Pay Monthly just to get this feature. It worked fine for the first couple of months, since then has been on and off.

[MI5]

@jrgloucester 

WiFi calling goes through a specific server at O2's end. I've noticed connection to this server can be sporadic and will sometimes go off for a whole day at a time.