wow! i came here not thinking i'd see anything related to this issue, but here it is.
i have an iPhone XS that recently, over the past month, has had a lot of LTE/voice signal issues. in places where i would normally have service, i get zero bars and zero LTE data. this has been most notable using Siri and wireless CarPlay where i can't get directions (using Hey Siri) due to no internet access. i didn't have this problem until recently.
i know that they are different phones, but my wife's iPhone 11 consistently has stronger signal than i have. there are times where i have had zero bars and she has two bars (both ATT) and getting fast data access.
i went to the Apple store today and diagnostics didn't come up with anything. they suggested the only thing to be done beyond "reset network settings" and DFU restoring the phone and setting up as new (tried both) is to get a new phone out of warranty...i may pursue this option if my credit card company approves my extended warranty request (i got a $549 +tax replacement cost from the Apple Store).
yet, i now am back to being suspicious that this is an iOS 13.3.1 issue. i can't recall when my issues began, but they did around the time i upgraded to 13.3.1
prior to the past month, i've never had any real concern about cellular signal with my XS.
