When I published this animation the other day, the movie was static until clicked. That opened a link to another page where the gif played and the image was very large. Apparently the size of the original files was the issue.
Thanks to Lemuel from the blog History Geek for telling me why it wouldn’t play automatically and for telling me how to fix the problem. If you are reading this blog you will likely find a lot to interest you at History Geek, so check it out here.