I have the latest software version 3.A.0084 but experienced this problem also before that update. When I’m connected to Wifi and somebody calls me (or I call somebody), the Wifi often disconnects (not always and not immediately), thus significantly lowering the call quality because I have bad reception where I live.
This happens with Wifi calling both enabled and disabled and interestingly lowers the call quality in both cases (even though I expect this only to happen with Wifi calling enabled). I also tried “Enhanced 4G LTE Mode” enabled and disabled, doesn’t change anything.