X750v2 will only connect to AT&T at 3G

Technical Support for Routers
2

Everything related to AT&T is in this post North American Carriers, ATT, Verizon, Cricket, T-Mobile Setup and Update 2021

But seems your issue is not listed.

What I am suggesting are:

  • first do a modem reset from the UI, then wait and see
  • then try the settings in the above post
  • third, try the following to lock 4G or auto using AT command tool provide on the UI

Choose network mode

set modem to only LTE

AT+QCFG=\"nwscanmode\",3,1

set back to auto

AT+QCFG=\"nwscanmode\",0,1

If still does not work, try the firmware here http://download.gl-inet.com/firmware/snapshots/20211227_3.211_beta4/x750/

The last firmware relate to a coming issue from AT&T. I am not sure if this relate to your issue but it is better to try and find.