missing calls : mobile app without wifi/mobile data

We have sometimes issues that when we have phone "standby duty" , we miss sometimes urgent calls because the app doesn't have (enough) mobile data/wifi coverage for a while in some regions or in the car.

On Android and Iphone with latest version

There is also no pop-up for missed calls.

Isn't there a setting who checks if mobile app is connected or not and if not, transfer to a normal gsm voice call withou voip if needed as fallback? This was possible in the old "myICmobile" app

* Are there somewhere logs to see if there was a lack of mobile data/coverage sometimes?