Last year I had this issue, and then again yesterday. I’m a long distance (miles) from the nearest cell tower which may make a difference.
For some reason, on AT&T if I set it to “LTE only” and “Auto” band selection, sometimes it gets stuck 3G. Yesterday it got stuck on “WCDMA Band 5 (850 MHz) 3G.” even though it was set to “LTE only”
I’m curious why with it set to “LTE only” it connects to 3G?
If I uncheck this band under custom band selection then it doesn’t get stuck on 3G.
(I should note that I had a similar issue with a cradlepoint 4 years ago at this location where it would sometimes lock onto a very slow 3G or slower band unless I did manual band selection.)