im having this issue constantly with iPhone 12 pro on ATT. I spent hours on the phone with upper level ATT support because I wasn't receiving text messages and data connection was dropping out and after a few hours they spoke with there engineering department who basically said its a known issue that ATT, Verizon and Apple are all working together on rapidly to try and pinpoint and fix. they said they had a similar issue back when the iPhone 8 came out also.