I was testing out some IPv6 only networks at home recently (not dual-stack), and I noticed that while Google and YouTube both support IPv6 (yay), the page loading was hanging for a few seconds, and only on Google Chrome. I looked at the network tools and found the following extension blocking the whole page load:

chrome-extension://pkedcjkdefgpdelpbcmbmeomcjbeemfm/

It turns out that this extension is the built-in media router for Google Chrome, allowing things like playing and pausing media from the browser UI, as well as relaying the media to Chromecasts. I don't know why it requires IPv4 networks (probably searching the LAN for Chromecasts), but you can disable it easily. Go to chrome:flags, then disable the following flags:

• Load Media Router Component Extension
  • chrome://flags/#load-media-router-component-extension
• Cast Media Route Provider
  • chrome://flags/#cast-media-route-provider