Yes, exactly the same boat and i've reached the same conclusion - i.e. some threshold seems to have changed so WiFi calling keeps dissapearing unless I turn on Airplane mode and then enable Wifi to stop it dropping back to something else. Basically, it only seems to work when connected to a really strong wifi signal if it has a choice of something else. I've tried using Wifi Selector to force a connection always to the strongest AP, which helps as I have multiple APs and otherwise android may well stay connected to a weaker one. Did you make any headway with this?
i have a samsung galaxy s9+. i was on android oreo and wifi calling worked fine. i.e. when i was home on my wifi, wifi calling would be active and stay active till i left.
I have since upgraded to android pie on my s9+ and wifi calling works for a while then drops back to VoLTE. I i disable 4g (and force the phone to 3g only) wifi calling stay active all the time. I'm guessing some sort of wificalling / VoLTE threshold has changed. is anyone in the same boat?
I seem to be having a similar problem as you. Since (unfortunately) installing the Wifi Calling Ap, I now have the BT wificall legend at the top of the phone all the time and no 3G or 4G. I was in an area where the home had lost its internet connection. There was no wifi hotspot and I could make no calls or receive texts during this time. Which meant I couldn't contact the Mum of the children I was looking after. It was worrying and very frustrating. I contacted BT who said the area where you live has 3G but little 4G, but 3G only worked when I disconnected my phone from the internet. BT wifi call has disrupted my phone and now it is not as efficient as it was. Apart from disabling BT wifi in the settings on the phone, how do you actually get rid of it all together so that 3G and 4G works again and the legend at the top of the phone disappears? I'd delete the app but concerned the problem would still be there with no app to support it making the situation worse.