Wi-Fi calling not maintained reliably - Moto G8 Power Android 11 & Moto G7 Play Android 9

[OJStroud]

We get no mobile connection inside most of our home, we've been reliant on a Signal Assist box for that last few years which has been great, but unfortunately the service is soon be terminated 😞

I've tried turning the Signal Assist off to test Wi-Fi calling, and both of our phones support Wi-Fi calling, and will initially connect and work successfully. However they don't reliably stay on the Wi-Fi calling. I'm not sure yet whether this is a time-based problem or more a case of if we go away from home then come back that it won't reconnect reliably.  

Once the Wi-Fi calling connection is lost, it's not easy to get it back. Turning the setting off and back on doesn't work, Wi-Fi Off/On, Airplane mode on/off similarly fail to reconnect and even rebooting the phone. The Wi-Fi connection is fine, just not Wi-Fi calling. The only way I have found to reliably (so far) reconnect is to turn Wi-Fi calling off, reboot the phone, then turn Wi-Fi calling back on. 

Any suggestions to try to make this Wi-Fi service more reliable please?

Does anyone experience similar symptoms to know where to start to find the problem?

Moto G8 Power (Android 11) bought SIM-free (from John Lewis) 
Moto G7 Play (Android 9) bought SIM-free (not from BT)
BT Mobile SIMS
BT SmartHub 2 (using Digital Voice)

[rbz5416]

As well as turning WiFi Calling on/off, some phones allow you to set which takes preferences. So check if yours has & if so, set it to prefer WiFi over 3/4G.

[OJStroud]

That's a good point. Can't be 100 % sure what I had set when I had big problems last week, but it's definitely set to prefer Wi-Fi for me now.  Will keep a close eye  on how it goes. Unfortunately doesn't appear to be an option on my wife's older phone.