I suspect reformatting has nothing to do with the real problem.
My problem remains fixed after the software update.
I suspect that the original problem was caused after a software update and that my LTE modem probably did not restart properly. But now, after the last update it has behaved normally (as it used to) presumably because the modem restarted okay this time.
As reported elsewhere on this thread, the identical problem would be caused by a dead LTE modem or a sick SIM. But I would expect those to only be a small percentage.
There could also be a glitch in the communications between your App and the Tesla servers that do the wakeup SMS polling. So, if I was you, I'd be taking the car somewhere outside of WiFi range but with mobile reception and seeing if your LTE is working (indicating on screen and allowing you to connect to the internet). In my case, it had stopped working but I did not notice because I was just driving locally and using DAB radio and nothing much else.
Then if the LTE is working, I'd check out your networking and your phone, which are probably fine.
Then if no joy, log a service call. A full hardware reset might work but I'm not going to suggest that.