v6p9d9t4.ssl.hwcdn.net is the domain for our HTML5 CDN, ssl.hwcdn.net is too broad so it should be avoided. We plan to migrate HTML5 games to to *.itch.zone at some point, but we’ve held off for quite some time now because of potential issues, but you can also add it for future proofing.
Here’s a page with an itch.io embed on a different domain: https://leafo.net/itchio_embed.html