Can you please make sure you’re running the latest version of WordPress 4.8.1, Yoast SEO 5.3.2 and your theme?
If you are already up-to-date, please check if the problem is still the same when all non-Yoast plugins are deactivated and your active theme is on Twenty Seventeen?
If you are unfamiliar with checking for conflicts, we wrote a small guide that will walk you through the steps. You can find it here: How to Check For Plugin Conflicts
I think it’s a problem with Gantry. I found the issue here:
http://www.rockettheme.com/forum/configuration-and-security/270064-yoast-seo-stopped-working?start=0#1359916
It seems to be a problem with mootools. If I remove mootools, YoastSEO seems to work
There’s indeed a conflict between (old versions of) MooTools and Yoast SEO. You can find additional information in this KB article: https://kb.yoast.com/kb/conflict-rokcommon-library-roksprocket/ Unfortunately, there’s nothing we can do to fix this.
There was a new release of Gantry today which fixes issues for the Gantry related pages: https://wordpress.org/support/topic/conflict-with-yoast-seo-24/
But Yoast SEO itself isn’t working yet. Is there a way to remove mootools from some backend pages (like posts)?
The Yoast plugin does not use Mootools, so there must be some other plugin causing the conflict. You can check for conflicts to find which plugin is causing this.
Yes, it’s caused by RokSprocket from Rocket Theme.
Yo can see it here: https://wordpress.org/support/topic/conflict-with-yoast-seo-24/
@tiiunder Since it’s an issue specific to the RokSprocket from Rocket Theme, we suggest you please speak to the relevant developer for assistance. They’d be the best place to assist you.
In addition, you can forward our this guide to the relevant developer.
