Nighthawk MR1100 Firmware update on 09_17_2018 causes mobile broadband disconnect

After firmware update NTG9X50c_12.05.05.00_ATT_03.12 was pushed to my router I am now receiving Mobile Broadband Disconnected when I am in a rural location.  When I bring the router back to the metro area it works just fine without any issues.  Any idea how to get my connectivity back?  AT&T seems to think it's a hardware issue but it seem coincidental it happened right after this firmware update.  Factory reset does not resolve the issue.  New SIM card did not resolve it either.