No data w/ 2-3 bars LTE

I switched to Xfinity mobile a few months ago, and have had consistent issues with data connectivity on my iPhone 12 pro. In much of the area around where I live my phone will show 2 or 3 bars of LTE signal, but be unable to get any data or connect to the internet at all. In fact, on my commute to work, from the time I leave my home wifi I will not be able to receive any data until I get to a specific point about 3 miles away. I know this because I use pandora radio for music, and I will spend 10 minutes in silence each day until I hit that exact point and the song can finally load. It's not just pandora, other apps will show no connection, email inbox won't load, and Speedtest will error out like there's no internet. It's not just my phone either, my wife's iPhone 12 mini does the same thing at various places on her drive. Again, this is with 2-3 bars of LTE showing. I also know it's not just the coverage, because I've previously had Verizon and T-mobile, and neither service had this problem. Since I know Verizon has the towers, and xfinity uses those, why can't I get any data at all? I'm not asking for high bandwidth 5G whatever here, just a reliable connection with maybe 1 Mbps? 100 kbps? Anything at all? What could be causing this, and what is the solution (other than switching to another carrier, which I'm strongly considering).