If this issue happens on your WordPress site too then one possibility is that your host doesn’t allow wp-comments-post.php to run. It happened to me once, and sadly I don’t understand the reason why.
Fortunately I found a working solution, as follows:
- Find wp-comments-post.php file inside your WordPress folder. Make a backup of this file first.
- Rename wp-comments-post.php file to something else e.g. my-comments-post.php
- Go to /wp-includes sub-folder, locate a file called
comment-template.php. Backup this file too and open it with a text-editor software e.g. Notepad++
- Find and replace “wp-comments-post.php” text with “my-comments-post.php”.