Have been having issues lately and did some deep trouble-shooting today.
All the usual trouble shooting, restart reboot gate way, reboot router, reset gateway, reset router, unplug devices, etc…
Found the issue was the gateway kept reporting it was connected but the router which is wired directly to the gateway said there was no connection.
I normally use an alternative dns provider for everything, as the ISP provided dns is slow and insecure subject to dns jacking.
As soon as I switch the router to use the ISP Provided dns from the gateway it connected perfectly, devices that were manually configured with the alternative dns on their interfaces still couldn’t connect though.
Switching these devices to the ISP Provided dns solved their issue as well.
Only thing that is working with the alternative dns without issue is the Secure DNS protocol which appears to be immune to what ever is going on with the t-mobile ISP.
I don’t know if this is a bug or a feature in t-mobile’s book or this is due to their main internet gateway provider somehow getting jacked.