Unfortunately, this is a new error that seems to be affecting TubePress galleries sourced with YouTube playlists. It appears that YouTube has changed something on their end. We are aware of the issue and working as quickly as we can to resolve it. Please stand by for updates.
@spavar1@jkwent We are expecting the fix for YouTube playlist-based galleries to be rolled out by the end of the day. Please watch this thread for further updates.