Strange problem with my Xfinity Mobile App

FOLLOW UP: With the help of Xfinity Support, I learned that the Xfinity Mobile App had indeed gone crazy earlier today, but only temporarily. It was communicating with the wrong server, as far as I could understand, so it was completely oblivious to my userid or my account.  So my userid, that has been the same for 30 years, was rejected as invalid. With telephone help, I was able to set up my mobile app again without a problem. All is well that ends well.