MY LG V30 stopped working on WiFi calls after the 20a System updated. I worked with Verizon chat folks for a while, tried this, tried that, still WiFi calling would not work . It would try to activate, then time out saying "WiFi Calling unable to connect, Try again later. Verizon recommended a factory reset, but I did not want to do this meaning I would have to reinstall apps, contacts, etc. WiFi in and of itself did work. I could connect to a WiFi server at my work, and transfer data, no problem. So I did have a WiFi connection but could not make a WiFi phone call. In settings, going to Network & Internet, then Advanced Calling, and then WiFi calling it would not activate. Then I called LG Support, no help, they said it is a Verizon thing. So I looked at every app by Verizon, and I found that two apps "Verizon Services" and "My Verizon" were both disabled or stopped. So I ENABLED those two APPS and voila, WiFi calling began working fine as advertised.
So it is important to note that if you have a Verizon LG V30 phone and you disable or force stop the "Verizon Services" and the "My Verizon" Apps, WiFi calling will not work.