It is simply hosted through Wordpress (going to upgrade to Premium at some point, but it's not self-hosted regardless).
I'll give switching themes a try.
Edit: I'm using the simple Twenty-Sixteen theme. Tried 3 others, and it will not embed.
Does the free-Wordpress not allow Itch.io? Like I said before, it's fine with Youtube embedding... so this would seem arbitrary and weird.
I had this problem, I've got an up-to-date standard self-hosted WP and it just seemed to eat up iframe contents where the src was itch.io
A colleague suggested I looked at plugins, and I used the popular 'advanced iframe' one - and that works great!
Pretty-much just pasted in the code from the itch.io widget generator, and dumped it straight into a post in my WP blog, and it works. I've not tried playing the game 'in the widget' - I'm happy having the user see the widget banner and click to go through to my page on itch.io itself.
