I think the problem is that I've signed up for a 10-day free trial of YTTV and 4K Plus, and I'm also using a secondary non-2FA account as a family group member on Google, per the recommendations of ChatGPT.
When I look at the CDVR troubleshooting log, the vast majority of Channel scan failures were "Not Authorized: You are not authorized to view this content."; "access.denied.missingpackage:" (the latter looks like it's pertaining to the Discovery channels); or "not entitled: mvpd: Resource is not support by MVPD" in the case of FS1 and FS2. Meanwhile, I think the only channels that scanned in successfully were probably ones that just don't require any kind of authorization.
When I opened up a window of Chrome's incognito browser (so webites wouldn't get confused by all my Xfinity provider authorizations), I was able to get authorization on ABC.com and ESPN.com for YTTV, but on ESPN everything I tried to play said I was not authorized to view this content.