Hey @stellabelle, I have been working with GIFs the past couple of days for my own content and noticed that as long as I'm saving them properly as animations, they work fine within blog posts.
I've begun to speculate as to whether there is something in the page build that prevents the animations from being viewed within the header portion of the blog pages. (It would make no sense otherwise, why an animated GIF would work within the blog posts, but not the headers of the blog itself.
I'd love to see this adjusted. It would be a hot feature.