I've the same issue going on. In my case, my Norton account which was linked with Xifinity is not working for some reason and Norton support acknowleged the trouble. However since last 3 days they have not been able to fix it for me. It maybe a similar problem for you.
I believe the problem at Norton end .. maybe account migration or something going on which has broke the linkage.
Today I contacted Comcast support but no response yet. Hoping they will help in some way.
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