I've had Channels working with Youtube TV since the beginning. I had a secondary google account setup in my Family group with 2-Factor Authentication (2FA) turned off, and it worked great.
For some reason I noticed my Channels DVR was not recording any new shows, so I logged into the admin page, and decided to Rescan. That's when I received an error about authenticating. I remove the account and re-added it to Channels. What is happening now is Google is doing a "Verify It's You" check since it's seeing this login from a different location than where I am, even though 2FA is off.
I decided to try a new Google account, linked to my Family group. Also with 2FA turned off. Same error.
I have submitted this information, along with logs to Channels support. Hopefully they will have some ideas.
For everyone still having it working, I suggest you don't rescan.

