Had some channels stop working, but I figured out what was causing it and thought I'd share.
I use a sub-user, Channels-only, account for the dvr. Yesterday I noticed I was getting 2-factor type texts when I tried (and failed) to watch certain channels. I had done nothing to enable 2-factor authentication on this sub-user account, but apparently Xfinity just decided to require it. The only way to disable this was to remove the mobile phone number from the account, which I did. But it still didn't work. Then I saw that the user account was a "manager" account that had billing privileges, so I downgraded it to a "member" account, and it seems to have fixed everything.
probably common knowledge around here, but thought it couldn't hurt to share.