If you are experiencing a 404 error on your wp-comments-post.php when using WordPress comment system, you can follow these steps to fix it.
- Update your theme to the latest version.
- Update your plugin to the latest versions.
- Update WordPress Core to the latest version.
- Make sure your wp-comments-post.php file permission is set to 644
- In the Admin Dashboard, Go to Settings > Discussions and enable “Users must be registered and logged in to comment“.
- Go to Settings > Permalinks and Resave your Permalink.
- If the above still doesn’t work, it could be a web hosting security issue. To test it, try using a similar plugin and it produce a 404, it means a web hosting issue. I personally use IMH but would also recommend you use WPEngine if you have the budget.
WordPress security prevents uploading of multiple image for non user the reason you are getting 404 especially when the user is not logged. This is a permission issue with WordPress. You can try modifying the user role using a role editor plugin “User Role Editor” by providing non-user with the same role permission or privileged as a subscriber however I generally would not recommend it to avoid spam and other security issues.