Relevant info: iPhone 5, ios 6.1 (jailbroken)
Updated to latest version of youtube app (188.8.131.52=804) which I think initially was working. Then recently I used google's "sign out of concurrent sessions" feature to sign out of about 500 logins across various devices. I have 2-factor-auth on also.
Anyway, now I can't play any videos on the phone. Signed out or signed in. Any video I try to play just shows me a black screen with "Playback Error" and the smug cat logo. I tried the things I found on their iOS help page which included changing network settings, trying wifi or LTE, and signing out, uninstalling, then reinstalling.