Wifi Call and one-way audio on iOS14

All,

I am facing a strange symptom using Wifi Call on my iOS devices (affects multiple iPhones)

Regardless of receiving or making a call, often I cannot hear the caller but the other side hears me.

So some kind of a one-way Audio connection.

Disabling Wifi Call fixes the issue.

I am not restricting any ports on my Internet Router.

Any ideas if this is a known issue with iOS14?

thanks

Mike