WiFi Calling not working suddenly

I have been a T-Mobile customer for many years. Wi-fi calling worked perfectly until a software update from T-Mobile around the middle of 2020 --  and it has not worked reliably since then. This same problem exists on many different makes of phones - Apple, Samsung, etc. I too live in an environment with poor cell coverage and have long depended on wi-fi cell phone connection with T-Mobile. Since that "update" my T-Mobile phone refuses to remain in the "wi-fi preferred" setting and constantly reverts to "cellular preferred" sometimes just minutes after I select "wi-fi preferred".  Sometimes Wi-Fi works, but I never know if it is working or not. Worse yet, OFTEN wi-fi incoming calls go straight to voice mail and my phone never rings. These problems have been brought to T-Mobile's attention over and over. The same issue occurs on various wi-fi networks. For a long time T-Mobile denied there was a problem. And they have tried blaming the phones, other apps, wi-fi networks, etc. In fact I have tried different phones provided by T-Mobile - but ALWAYS have had the exact same issue - meaning this is a software issue. It really needs some high level technical work. It should be very easy for T-Mobile to explore the problem by setting up a panel of many different phones and observing the issue at a test center. The other answer is to stop advertising wi-fi as a reliable available communication method with their cell phones. Such as advertising  "it is sometimes possible to connect on a wi-fi network." But not reliably so. To advertise the service, and have it not work properly for many months, is a dangerous situation for users like me. I use an Android phone but see many on-line complaints from Apple users. To deny that the problem existed, in the past, was irresponsible and dishonest. You can delete cache, and turn anything on and off.. it won't help. Something is deficient in the operating system… a CHANGE from what was working PERFECTLY prior to the abominable update. Every T-Mobile customer who uses or depends upon wi-fi connectivity should be reporting whatever difficulties they are encountering. To me - the wi-fi issue is a much more significant one than 5G availability. Once we start traveling internationally, the unreliability of wi-fi connecting could be a costly one to us, as well.

I just used the Ookla Win10 app to test my Internet connection via WiFi. It tested to a server in Honolulu. It is prime time here.

Download 149.55 Mbps (a drop in download at prime time is common in my limited test experience)
Upload 21.83 Mbps
Ping 12 ms
Jitter 29 ms
Loss 0.0%

Several more data points:

1. WiFi Callng to/from our iPads via “Call” not FaceTime is working in/out--so I conclude that the issue is not with T-Mobile WiFi Calling in and of itself.
2. The phones, after being put in Airplane Mode, and then turning WiFi back on, also place and receive T-Mobile WiFi Calling calls.

So, it seems as if the phones are not falling over to WiFi Calling when the wireless network is enabled but of insufficient signal strength to use.

I should add, FWIW, the Apple Store phones were Carrier Free (unlocked) and brand-new SIMs were ordered from T-Mobile with service.

Have you tried resetting network settings on each iPhone, then re-enabling WiFi calling? It's a basic troubleshooting tip, but sometimes the simplest thing can resolve issues. 

I have not, for two reasons (of arguable validity and, possibly, ignorance):

1. WiFi otherwise works on both devices fine and, indeed, if the Wireless is off and WiFi is on, WiFi Calling works on the devices fine as well.
2. My decade of experience with Android tells me that “Network Reset” on the device is *very* destructive of things like all Bluetooth pairings as well as all remembered WiFi networks.

The latter, for me, is really a deal breaker. I can't say what this does on iOS as I've never tried it on the iPads I've had for years, nor on the iPhone which I've only had for six months now. Maybe iOS is different. When I got conned into it several times in my Android life, it fixed nothing. And it broke lots of things. My iPhone, for instance, has 18 BT pairings. That's hours of effort to get those all setup and tested again. There's no way to tell how many WiFi networks iOS knows about. But it's probably not as bad of a situation as my prior Pixel 2 was--it had over 50. Now, I knew for sure that lots of those were overcome by events and would be no loss. But which ones?!? And what of the others?!? If I had reason to know a Network Reset would fix this--other reports of people with the same problem solving it this way, say, I'd try it. Just on an off chance a miracle might occur? Life's too short.

On iOS/iPadOS, resetting network settings only resets cellular and WiFi settings, as well as location services; Bluetooth settings are left intact. I've never dealt with Android, unfortunately. Definitely sounds like a weird situation. 

Had a Moto X{2nd gen} and Moto G7 Power on Republic wireless and used our home WiFi extensively as cell service stinks in our area.

Just switched to T-Mobile with 2 new Moto G Stylist 5G phones, which, in town, get 5 bars but at home, 1 bar is the best if we get it.

When attempting a WiFi call with one or both phones in the house on Wifi only one side of the conversation can be heard. Reset both phones & router, verified the router was assigning an IP address to both but my Wife can hear me but I cannot hear her. Only when both phones are on cell only, WiFi shut off/ T-Mobile WiFi also shut off can both sides of a call be heard.

This lack of WiFi is rendering T-Mobile and our new phones useless as we are in a weak T-Mobile coverage area and if WiFi is on, IF we actually get a call, only one side of the conversation is heard.

If anything it would be a benefit to T-Mobile to have as much traffic over WiFi as that frees up more bandwidth for cell service. A WiFi call in my case would go over Spectrum's network.

As we spend 90% of our time at home, WiFi must be available. It was until I switched to T-Mobile.

Come on, we put multiple men on the moon and we can’t get WiFi to work?

Maybe relying on “off shore” programmers is not the best tactic.

Same issue happens about daily around 10am EST. I don't get a reliable cell signal at home so wifi calling is always in use.  I restart the phone and wifi calling works again. 

I've fought this problem for hours over the past several months on both my phone and my wife's.  They even sent me a hot spot tower and it's didn't work either.  I've finally made the decision to go to another carrier.  I don't know what the problem is and apparently T-Mobile doesn't either but I never had this problem before I switched to T-Mobile.  I realize not that is was a mistake on my part.