Hi. I think they have changed the way wifi calling works on this update. I'm on ee with a unlocked s9+ and I notice in my house I rarely ever have WiFi calling now (was there all the time on oreo), instead it stays on Volte. I suspect its because I have a strong 4g signal. If I force the phone to use 3g only (removing volte) it connects and stays connected to WiFi calling in my house.
I have found a solution which work for our phones.
I turn off the VoLTE in the settings and the WiFi calling start working instantly.
I turn the VoLTE on again and the WiFi calling stays on.
Just one thing I notice is if you turn the WiFi off and on again it takes more time for WiFi calling to turn on than with the Oreo.
Hope it will work for others as well.
Seems like everyone else in the world got it, but not vodafone uk. They said January, why say it if they didn't mean it? Lots of other vodafone regions have it so what's the problem?