iPhone 11 stuck on Edge/2G

Hello all.

I switched from an iPhone X to an iPhone 11, 2 months ago.

When i go to my building's parking to start riding our car, the iPhone goes on Edge, after leaving the building, it doesn't turn to LTE again.

Even if i deactivate Data connection, and turn it on again it comes back to Edge.

The only solution is to turn on the Flight Mode, and then off, and as soon as this happen LTE comes back.

(i'm pretty sure that there's nice LTE signal just into the door of my building, because if i do this procedure there it works)

Any advice?