WiFi calling problems

My WiFi calling isn’t working correctly - is this a bug? I have the new iPhone Xs, and 400+Mbps broadband internet speeds but virtually no cell phone signal in my home. In “normal” use the phone always tries to use the little-to-no cell phone signal and then the line is horrible, unless the call drops completely. I’d rather it use my strong WiFi signal for the call but it seems the only way to force the phone to select WiFi calling is to switch to airplane mode, (and of course make sure WiFi stays on). Occasionally this works well (so yes, all my settings are apparently correct), but frequently I have to wait several minutes in limbo before the call either connects... or fails completely. Worse, maybe half the time I get this message: “No Network Connection - Connect to a WiFi network...” - while at the same time showing that I already have a GREAT WiFi connection! Here is a screenshot of it:

I used to have an AT&T Microcell, which was great, but it was discontinued and I was told not to worry because the iPhone WiFi calling would work even better. Instead I’m really worried because I’m missing calls and unable to call out probably 50% of the time right now.

PS - Yes, I’ve tried turning off WiFi calling, waiting and turning it on again. Yes, I’ve tried turning off WiFi completely, rinse and repeat. And yes to rebooting the phone too. Any of these might or might not work on any given occasion - and might work for one call, but not the next.