Since Yoast SEO 3.0 Page Builder is not working anymore for me. The tab is gone in the editor. The pages that I made with the page builder do still function, but I can’t make new ones.
Again clash with Yoast Seo
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This is rather old but may help. In one case, someone had extra code in functions.php in another scenario, enabling, disabling the plugin helped.
https://wordpress.org/support/topic/plugin-wordpress-seo-by-yoast-breaks-the-tinymce-editor-on-html-tab
There was a problem with Yoast clashing with several plugins after the 3.0 update. They were able to fix most of the issues with some updates. If you’re running the latest version of WordPress SEO (3.0.6) and are still encountering a problem, let us know and we can try diagnose the issue.