Deco Mesh and New Connection Problem to Gateway

Greetings  Thoughts Appreciated

So my T-Mobile Gateway Internet and Deco Mesh system have been working perfectly until 2 days ago.

Making this simple

Contacted T-Mobile 2x and went thru all their recommendations and then contacting Deco following their recommendations also.

So here is what’s going on.   

1. when I disconnect the Deco Mesh system from the Gateway the Gateway works just fine - but of course no mesh system.​​​​​​​​​​​​​​  

2 T-mobile says there is a problem with the Tower that supports my Gateway internet.​​​​​​​

3 But yet (again) when I do not have the Deco Mesh system connected the internet is working.

Any Thoughts 

Austin Texas