This is now fixed! The gifs will be converted to webp, but they will now be animated (webp also supports animations).
However someone will need to upload the gif again.
Sorry, the reason is that the add-on doesn’t upload the media file because it was already uploaded. So it uses the old image. I can’t immediately think of a good and easy fix for that. If there are not that many notes with this problem I could fix them manually if you send me the file.
One workaround for this is to change the image slightly (by using an image editor). Then the add-on will treat it as a new image, will upload it and the animation will be shown.
Note that you may need to delete the local storage of your browser for the AnkiHub website in order for the animations to show on the website immediately.