XR500 - WiFi Calling Stopped Working?

Hi Folks,

I recently bought a new NetGear CM1150V Cable Modem and XR500 Nighthawk Router to replace my XFinity Cable Modem/Router as I was having major problems using my iPhone's (AT&T) in my home for WiFi calling in Airplane mode. In addition, I got a new iBuyPower Gaming PC with a 1000 mps LAN port and the XFinity router only had a 100 mps port (I have the Burst 350+ mps service)

I was super impressed how easy everything was to setup and install on both devices from NetGear. After completing installation and per the recommendation of the Netgear Router setup wizard I used my previous XFinity Routers SSID and password (which would make my life a lot easier). After completing the installation, I rebooted our two iPhone 6S Plus phones. They logged onto the NetGear WiFi and WiFi caling was working perfectly with the phones in Airplane mode (an AT&T technician had previosuly told us to use Airplane mode + Wifi as our cell service here is only 1 bar. This prevents the Cellular system from competing with the WiFi all the time).

Fast forward less than 24 hours. Now both iPhones in Airplane mode + Wifi cannot do WiFi calling, so my phones are worthless for making or receiving calls while we shelter in place during a pandemic. The only temporary fix that I've found so far (which is not consistent) is turning off Airplane mode and going back to Cellular Data being On with WiFi. The problem is I'm still missing calls, and if I do make a call, I cannot move anywhere else in our condominuium without potentially losing the call, which was exactly the same problem I had before with the Xfinity Modem/Router. What happened? Why did it work for the first few hours and now it doesn't? While I'm thankful that I can now get 380+ mps on my new Gaming PC, not being able to use WiFi calling on my iPhone's is a real problem.

I've seen several postings here in the Community on this topic, but no single working solution seems to have been provided by NetGear or anyone else for that matter. If I can't find a solution, I will be forced to get new iPhone's from a different carrier (we moved from CT to FL) and lose my AT&T previous company's 22% discount and have to pay more for new iPhone's. Being on social security disability now, I would have preferred not to have to go this route. Any and all recommendations and solutions would be greatly appreciated. I hope that one of the NetGear guru's also takes note of this thread with the correct expertise and can offer a working solution. Thanks in advance.

Roger