Thanks @gvectorssupport for your prompt reply. I have verified all the steps mentioned in that page. I am sharing the observations.
1. I do not have other comments plugins such as Disqus and Jetpack comments
2. The default form is enabled for Post, Page and Attachment
3. Under Discussion settings, I have the checkbox enabled for allow people to post comments on new articles
4. On the edit post screen, I have Allow Comments enabled
5. I do not have custom post types
6. I am sure the template I used Spacious uses comments_template() since rest of the sites in the multi-site network uses the same theme and for those wpDiscuz comments is working properly
Note that, I have Elementor plugin installed, can that interfere? Please note that I am seeing default comments section instead of wpDiscuz comments.
