Several of us have exchanged our phones for another phone. Several have replaced the SIM cards. I'm on Verizon and you're on ATT. It's clearly not caused by any of these nor can it be corrected by resetting the phone, switching on and off WIFI etc.
My educated guess is that either Apple used a different GPS chip and antenna in the iPhone X that's more prone to interference, or as JLLKK said, the glass back allows more electronic interference from the instrument panel area to get into the iPhone X and essentially jam the receiving of GPS satellite signals.
I do have a case open with Apple support. I recently sent some videos of my app not working for lack of GPS and I've forwarded a synopsis of the comments on this thread.
I don't expect they will formally acknowledge the problem but maybe they'll be able to define a fix such as a back cover that electrically shields the phone better from the interference source.