I noticed in your documentation that the add topic button is supposed to open a rich-text editor like the one I'm using here. My add topic button gives a bare editor without the formatting bar, so I can't add links.
I have turned on debugging mode if it helps. The site is live at ontheten.org
Got it to working now, it was the Autoptimize plugin conflict. Just uninstalled it. Rich editor working now.
Sorry to bother you.
Rather than uninstall it (because it is a very good plugin), you can add: tinymce.min.js to javascript exclude list and you're set.
Ewscos. It's possible that it conflicts with other plugins, absolutely. You'd need to test which javascript is causing the problem and exclude it. Took about 10 minutes to do for wpforo and Autoptimize has been pretty good with my other plugins (over 30). Unfortunately, if you don't know which plugins are breaking it then it could take a while to find the answer. I use a staging site for testing this sort of thing (so my live site doesn't break!).
Take care.