I decided to try a T-Mobile after many years of being on AT&T. The T-Mobile account I tried did not allow tethering. When I was done experimenting with T-Mobile, I put my old AT&T SIM back in, and when I reconnected to the AT&T network, I could not tether and I have not had tethering since. Have tried numerous troubleshooting steps, to no avail. Never had a problem with tethering before connecting to T-Mobile network. This is Android 8.0 and unlock, unbranded Motorola XT1650, Moto X2.
Question: is it possible for a carrier network to issue commands that permanently disable tethering, and to make them stick even after reboot?