Hey Eric, thanks for your patience. The behavior you're seeing is a combination of the X-Frame-Options and Content-security-policy headers from your sites.
Ironically, each of the three URLs you're using have different policies. I'll followup with you to give you specifics; but in short, the policies on the docs and events sites should allow embedding, whereas the matchmaking site will not.
As to the discrepancy of why I was seeing that behavior in my browser but you were not, it could be due to a number of individual browser-level configurations... but it may also have to do with our own CDNs serving stale data, which I will look into!
