I can also confirm that I am experiencing the same problem with my X750 on Cricket, which uses the AT&T network. I have 5 lines on a family plan with one of the SIM’s being in this router. All phones in the house connect to LTE just fine, but the router never does (only 3G/4G, which limits speed to 3MB/s). When taking the SIM card out of the router and putting it in a phone, it connects to LTE with no issues. There appears to be some compatibility issues with the X750 and the ATT network currently.