You said it was fine until you started using a VPN?
Maybe that is causing the issue.
If a forum member gives an answer you like, give them the Kudos they deserve. If a member gives you the answer to your question, mark the answer as Accepted Solution so others can see the solution to the problem.
What are your credentials? Do you understand why dude doesn't get bounced when on VPN?
The use of a vpn is often times not allowed on certain isp’s. Verizon Fios may allow the use on a limited basis. It can be the setting on the customers routers that are making YouTube buffer etc. let’s not blame the broadband isp for the issue.
and try setting changes to see if that improves the situation.