There is an issue in the back-end that the Search Engine Visibility Checkbox is disabled and I'm not able to check or uncheck the checkbox.

What is happening that when I load the page then it comes normal but at the end of loading it will appear like in below image.

I have uninstalled my all plugins and renamed the plugin directory too, but this issue still persist.

_{(source: plego.us)}

robots.txt Code.

User-agent: *
Crawl-delay: 1
Disallow: /wp-content/plugins/
Disallow: /wp-admin/

Any help will be appreciating.

Thanks