I'm sorry to don't see this game as HTML5 because I am not able to rate it.
I love to use C2 too, I keep using it in 90% of my projects, unless they are clients' work, so I was happy to see others keep using it.
Have you tried to export a simple project in HTML5 to see the issue? Just put the text object, without any plugin and see if that works. It's a while I don't export for HTML5 and upload on itch.io, but I think C2 still works fine.
Do you have the latest version?