A few people have noticed their AT&T branded Netgear Nighthawk mobile hotspots recently prompting to install a mandatory firmware update from AT&T - version: NTG9X50C_12.05.05.12
This seems to be a very minor bug fix release, and it is perhaps caught in a time warp - AT&T's page on the firmware says that it was originally from December 19, 2018.
Jan. 21, 2020 Update: This new release has an Ethernet bug that is preventing some users from utilizing the Ethernet port. Netgear is aware of the issue and is working on a fix.
Feb. 12, 2020 Update: AT&T pushed version 12.05.05.14 to fix this bug.
The "What's New" listed is relatively insignificant:
Confusing things - in November 2019 Netgear released an update labeled as 12.06.08.00 for the Nighthawk MR1100 that includes a fix for reboots when running without a battery installed. This update is for the non-AT&T branded unlocked Nighthawk models, and is newer than what AT&T has now released.
Perhaps AT&T pushed the old minor 12.05.05.12 to lay the groundwork for an imminent official update to 12.06.08.
- New Firmware Version NTG9X50C_12.06.21.00 Rolled Out for AT&T Netgear Nighthawk Posted on: March 2, 2021
- First AT&T 5G Mobile Hotspot Available for Consumers - Netgear Nighthawk 5G Mobile Hotspot Pro Posted on: September 16, 2020
- Verizon Pushes 2A Firmware Update to Inseego 8800L MiFi Jetpack Posted on: May 13, 2020
- AT&T Releases Minor Firmware Update 12.05.05.14 for Netgear Nighthawk (MR1100) Posted on: February 13, 2020