That is strange. You should report it to google's bug bounty program so that they can triage it or get it to a group that can fix it. (I'm not sure of another avenue to get through to a person there.)
If you asked the google bug bounty program about it, I'm sure they'd either answer for youtube, or send you in the right direction. While unlikely, I wonder if it was some kind of hash table collision. If you change your password again that might solve the issue if that was the root cause (a guess).
In terms of where to go from here I've no idea.