What is the "Hidden Network" showing up on my T-Mobile Home Internet and how do I tap into it?

I have a mesh network at another house, and the “back-channel “is a hidden network since you are not intended to connect to it (the nodes use it to pass data).  It could be that your TM router actually has mesh capabilities that aren’t being used, but the back-channel is still active.

Did you ever figure it out? I have the same thing happening; briefly my computer once showed around 6 or 7 networks (all named T-mobile...) and then it went back to saying Hidden Networks. No neighbors around me to pick up their signal so it's definitely all coming from my gateway 

Are you sure it’s from your T-Mobile gateway?  On my PC, I see a list of networks all around me.  I see two Hidden Networks, both labeled simply “Hidden Network.”  One is mine; the other is a neighbor’s.

To connect to a hidden network, you need to enter the SSID (Network name) in addition to the password.

You can create a hidden network for your own system.  In the app, there is a toggle to make a network hidden near the bottom of the Network settings screen.  

Link to Tutorial for Android App:

https://www.t-mobile.com/support/tutorials/device/app/android/topic/t-mobile-internet-app/how-to-create-additional-wi-fi-networks

Link to Tutorial for iOS App:

https://www.t-mobile.com/support/tutorials/device/app/ios/topic/t-mobile-internet-app/how-to-create-additional-wi-fi-networks/5