Youtube Previews Miss Play Button and Inline Playing: After updating to Discourse version 3.1.0.beta4, embedded Youtube videos stopped playing in old messages, instead displaying a clickable image. A manual Rebuild HTML on each post fixes the issue. However, for a mass rebuild, the rebake-all-posts-matching-a-pattern method can be used. Canapin warns against rebaking too quickly, as excessive Youtube requests can temporarily blacklist the server’s IP and break Youtube embeds.
A little warning about that. If you target only posts containing Youtube videos, and don’t set a timer between each rebake, it will make a lot of Youtube requests and your server’s IP might be temporarily blacklisted, leading to broken Youtube embeds.