Unable to access routerlogin.net

Hello

I'm a not a tech, I'm a beginner and senior citizen too, so be kind.

AT&T U-verse 5268ac GATEWAY dual band router

AT&T Cisco VEN401-AT Access Point (talks to TV boxes)

NETGEAR WNR2500RP-v2 (used as what I think you'd call a wireless bridge)

At my condo complex (1400 units) we all have AT&T U-verse wireless TV, and then we arrange for our own internet, so most residents use AT&T that broadcasts the 2.4 Ghz band on channels 1,4,7,10 , while others use Comcast that uses the 3 channel system that 1,6, 11 pattern. I typically see 14-20 SIDS on each channel, so WiFi speeds are around 3Mbs on 2.4 Ghz. On the other hand my 5Ghz wifi runs at between 84 and 118 Mbs.

In order to access the internet I went into AT&T's GATEWAY and renamed 5Ghz SSID so I can force a connection to this band that runs at about 84 Mbs, even though AT&T displays warnings against doing this. Then I use the NETGEAR in another room to connect to the 5GHz band and provide wired Ethernet to my two printers and my desktop computer. And I've got the WiFi turned off on the NETGEAR so this doesn't contribute to the WiFi Pollution. This has run flawlessly for 5 years, until one of the TV boxes died and I couldn't get the new box to connect to the VEN401. A service call was scheduled for the day after Christmas

On Christmas Eve, AT&T contacted me, they had made some equipment changes and wanted me to try again. No joy. After the phone call I found that AT&T had remotely turned off my 5Ghz band on my GATEWAY as their equipment changes. When I went to login to the GATEWAY, my computer crashed with some blue screen, yikes. But after I rebooted I was able to login to the router. After that my Windows 10 desktop had become unstable with the Start menu going missing about once every 2 to 4 hours, then 2 days later my Ethernet connection through the internet died. Tried the other ports on the Netgear, and of course rebooted everything. . Finally 2 days ago I computer crashed with blue screen that had an error message on it and was able to see something about a paginating error with a process that looked like networking. So in the device manager I removed the ethernet adapter and wifi adapter, rebooted and Ethernet and Wireless networking once again functioning on the desktop, I have not crashed or lost my menu in 2 days, but I still can't login to the GATEWAY or the NETGEAR from any browser, and yes I've cleared my caches.

Then this morning I rebooted the GATEWAY and before the process was finished I went into my office, and my browser was sitting on the NETGEAR router login page. After the GATEWAY boots up and the connection is made I can longer reach the NETGEAR which is connected via Ethernet, but this is repeatable.

QUESTIONS:

Is there some sort of security setting in the 5268ac GATEWAY that would prohibit wireless access to the login screen.

If there is a such setting trickle down to the NETGEAR and prevent me from accessing RouterLogin.net via Ethernet while there is a wireless connection to the GATEWAY? Or is this coincidence.

If such a setting exists what kind of terminology and settings area would this be, I have no idea what I'm looking for, I'm not a tech?

I think this is just a coincidence that my Windows 10 computer which was idling decided to crash and become unstable coincided with AT&T reaching into the router and turning off my 5Ghz band, and that it just happened to be fixed by reinstalling the networking adapters, but the timing certainly bothers me.