Drops on Nighthawk M1/AT&T Multiple Times Daily

Carrier:  AT&T

Model:  Netgear Nighthawk M1 MR1100 2A1NAS  (AT&T branded)

Firmware:  NTG9X50C_12.05.05.14

PRI Version:  04.06

The problem started a few weeks ago.  My unit is stationary with "fair" signal, which has been flawless prior (never needing rebooted for 6 months straight).

Now, about every 5-6 hours, the entire network stops being able to connect to internet servers specifically on ports 80, 443, and 8080 (all web ports) on the WAN side.  I am still able to connect to the hotspot's internal web server.  This happens across all devices on multiple tested web browsers (and even testing these ports with raw telnet fails).

However, pinging internet servers on the WAN side still works.  And I am still able to connect to internet servers on FTP (port 21), telnet (port 23), SMTP (port 25), DNS (port 53), POP3 (port 110), and IMAP (port 143), as well as any other ports, tested by using telnet to connect to any port on a test server, "portquiz.net".  (When using a command prompt "telnet portquiz.net [port number]", a successful connection is when the window goes black with just a blinking cursor.  If it does not go black and just sits there and eventually times out, "connect failed", then the port is blocked.)

I have seen a couple of other people with this issue on here.  Are there any other people experiencing this?  Because it only affects web ports, it seems intentional by AT&T or the hotspot.

A reboot of the hotspot (via menu on web interface) temporarily fixes this, allowing WAN connections to ports 80, 443, and 8080, again.  But the problem returns after 5-6 hours.  I have tried factory defaulting the device, but that does not help.  I do not have another unlocked hotspot to test the SIM in.