Hugh,
I took a backup from the live site and restored it to the dev site, the dev site should now work (tested). I added my live site info to my URL list for you to take a look as well, as that may be of use to get this issue solved.
The exact same copy of the site is on both the development and on the live site. On the development site everything is now working as expected - comment form with WYSIWYG working as it should, it also works without WYSIWYG option. But for whatever the reason, on the live site, WYSIWYG option on comment form doesn't work, only the non-WYSIWYG works on the live site. Keep in mind, these two sites are a copy of each other, no changes have been made. The live site is HTTPS and the development site is HTTP, I forced HTTP onto the live site and the WYSIWYG option still doesn't work, only non-WYSIWYG works.
How strange is this huh? In any case, I had to revert back to non-WYSIWYG on the live site so the users can enter comments.
I made identical accounts for you to take a quick glance on both sites. If at all possible, please keep in mind not to make any changes on the live site as users are on it. If you want to see the behaviour of how it's acting on the live site, first enable WYSIWYG option in the backend comment form plugin and then use record 711 in the front-end to try and entering a comment. When done testing, please revert back to non-WYSIWYG for comment form plugin so the users can use it again.
Thanks.