Lately I find my self with some number of bars on my iphone yet without a data connection. I restart the phone and data is restored. I have an iPhone 13 on RedPocket.
No experience with it, but maybe a shortcut for you to try. Instead of restarting, switch Airplane Mode on and then off again, should cause the phone to re-search for a cell signal. Might have to do with which tower you're connecting to.
Sometimes when I leave an area with no coverage (like a parking garage) it takes upwards of 10 minutes for my phone to recognize that there are cell towers within range.
I can kick it by toggling Airplane Mode off/on in the Control Center.