Sometimes you may experience that YouTube (or any other website is blocked) - you will see the website is blocked for no reason and it says you are logged in as (IP Address) - see the first image below.
If the website was being correctly blocked it would show who you are logged in as your username - as an example I tried to visit 888.com logged in as testteacher - which is a genuinely blocked webpage - you will see it shows the reason for blocking and the logged-in user as testteacher (second image below)
The reason is that there is someone else logged into the PC, so the filtering agent can only recognise one user logged in - you would, in this case, need to either log the other person off - but rebooting the PC would log all users off
