I started to have this issue on ny iphone12 pro after updating to tye ios 15, got in mail my bew iphone 13 pro max and i still have the same issue. I contacted apple support had me do several things including reseting network settings and some other things , contacted att had them reset the connection to the tower, and nothing got fixed… same thing is happened to both phones. Apple please fix the issue, since started to happen after the update has to be something wrong with it. thanks bye