The classic slider is not working properly with Yoast SEO. The response from Yoast: Unfortunately, there is not an easy answer to this question. By default, our plugin does not analyze content that is outside of the main content box of a page or post. Some visual composer developers have modified their code to add compatibility with our plugins while others have not.
If X Theme’s page builder doesn’t send their content to our page analysis or even breaks it, please reach out the developers of X Theme’s page builder and ask them about fixing the functionality to their visual builder.
Why Is This Not Included By Yoast? A while back, we tried to parse shortcodes and other plugin’s content but the outcome was a broken SEO plugin on a large number of sites. We reverted the changes and added a process for developers to parse their own content and push it into our content analysis.