Phone number sometimes showing as blank in settings, can't receive calls

I recently moved to a 2020 iPhone SE, including moving my SIM card. At first, everything seemed to go smoothly, but I've just noticed that sometimes when I restart it, if I go to Settings > Cellular, my number doesn't show up under the Xfinity Mobile section. Sometimes restarting my phone fixes it, sometimes it doesn't. If the phone does show the number, everything works fine. If it doesn't, I can't receive calls or texts and have no notification that that is the case. I'm sharing an Apple ID with a family member (the specific ID is on two devices, we're not doing family sharing), and although I've turned off the "Phone and FaceTime" setting in iCloud so we don't get each other's calls, some early searching says that this sometimes has something to do with iCloud not synching properly. Do I need to create my own ID and join via family sharing? I also didn't sign into the ID on the new phone and "logged in" through the data transfer from my old phone; should I log out and back in properly? If the Apple ID has nothing to do with it, is it possible that converting my old physical SIM to an eSIM would fix it?