[das-hinterland]

We don't know much about the OP's WiFi setup other than he chose to use his own equipment and not to use the carrier's gateway - which would broadcast its own, stronger, passpoint SSID in his apartment and likely these issues would go away.

Consider the following scenario: the OP's router is flaky and disassociates stations during which time the phone gets kicked off then "sees" the carrier's SSID from the neighbor and joins it. Now it's on that network. Suddenly this becomes a self-created problem. The solution is to not use Xfinity mobile or any other "Wi-Fi first" MVNO.