I have a Pixel 3a running Pie and wifi calling doesn't work. In particular, inbound calls to my phone (over wifi) result in audio only going *from* my phone to the caller, but not the other way. Turning off Wifi cures the problem and allows me to return the call.
This happens on two different Pixel 3a's on two different networks -- so it doesn't appear to be specific to the phone or the network.
Does anybody else see this problem? From reading other threads here, it seems that it is different to the other wifi calling issues (though there is an iPhone issue where the audio channel goes one way after five minutes).