As T-Mobile was rolling out 5G they dropped support for 3G and possibly some older standards/protocols. If you have an oldish phone that may be the problem.
I'm currently on an iphone 17 pro, and I am usually one a phone that is within the latest three release cycles.
I'm pretty sure I had a little of this before 5g rolled out, but I've seen a big spike in the ghost calls after 5g arrived.