Hot Spot stopped working

It's possible that you have the Hidden switch set to On. Use the T-Mobile app and tap the Networks tab on the bottom of the screen. From there you should see your network. Tap that and scroll to the bottom of the screen. There is a slide switch labeled Hidden. Make sure it is turned OFF, then Save your settings.

You may have to restart the gateway to have the new setting take effect, but after that you should be able to see your network.