Why is the "null" problem so mysterious

There are multiple examples in this forum of people descending into an infinite loop when trying to log on to the Stream App - 1) put in username and password, 2) send text code to your phone number accurately listed as ***-***-8127, 3) text code received on appropriate phone, 4) code entered, 5) returned to the "send text code" screen with the phone number now listed as ***-***-null, 6) scream again, and again, and again.

I REALLY don't understand this. Bought a brand new iPad. Stream app can not log on because of the infinite loop described above. I've spent 2.5 hours on 3 separate calls/chats with Xfinity support. They all behave as if they have never heard of this error. Even after I've asked them directly, they can not answer this question - have you not heard of this before? This problem goes back months on this forum. I really really want this fixed on my new iPad. The app is working on my phone and my OLD iPad without difficulty. XFINITY Support - PLEASE FIX THIS and PLEASE respond to me but PLEASE DON'T tell me to call the regular 800 number because I have not resolved the issue there - "we will escalate and get back to you" - which hasn't happened. I have 2 case numbers now. PLEASE DO respond to me if I can speak with someone WHO KNOWS THIS ISSUE and HOW TO RESOLVE IT. After 20+ years as a Comcast customer, this is just about breaking me.