Dropped service

I recently switched to Xfinity mobile with an unlocked AT&T iPhone X. It seems like during my commute, as I travel through different cities, my service disconnects and won't reconnect without me enabling airplane mode and disabling. I've talked to the folks at the store and they changed my sim card and still have issues. I took the phone to Apple and did a full restore and showed it was unlocked in iTunes and still same problem. This issue happens with my phone and my husband’s phone as well. I've also reset the network settings. This is driving me crazy and I may have to go back to AT&T