Thanks for checking. I think I see the problem. I will try something and get back to you about it.
Edit: this is what I think is happening:
Your posts are all being displayed on the WordPress posts page. By default, WordPress does not show any comments on this page. When you disabled all plugins and tried WP Discourse with the 2016 theme, no comments would have been displayed on your posts page because that is the default WordPress behaviour.
With the WordPress twentysixteen or twentyseventeen theme, to get comments to display on the posts page you need to add a line similar to this to the
content.php file. This goes below the call to
global $withcomments; $withcomments = 1; comments_template();
When I do that, I am able to get WP Discourse comments to display on the posts page.
Are there any single post pages on your website that you could check? It would be good to see if Discourse comments will appear on a single page.