Here’s a strange one – I have a small animation that is used for a Google display ad. It previews in Safari when viewed on my desktop. I uploaded to my web server and from there it displays properly in Firefox, but not in Safari. Same thing when previewed in AdWords - shows up in Firefox but not Safari.
Can you try ctrl + clicking on the area where the Hype document would be and then clicking ‘Inspect Element’ ? I feel like the developer console should be giving you some information or at least an error if nothing is appearing…