Can you please confirm you are using the most recent Yoast v7.0.1 You can learn more about updating here: https://kb.yoast.com/kb/how-can-i-update-my-free-plugin/
If you already confirmed the plugin is updated to the most current version, this may be due to a plugin or theme conflict. Can you try and gather as much information for us as possible? Please perform the following:
1. Make sure the issue doesn’t persist when Yoast SEO is disabled.
2. Check for conflicts.
3. Check for JavaScript errors with your console.
If you find any JavaScript errors related to Yoast SEO or if there is a conflict with a plugin or a theme, you can create a new GitHub issue for our developers. Please report the issue to a third party developer as well.
If you didn’t find any conflicts or errors, we think the issue is specific to your site. We’d need to investigate further but are unable to do so on these forums. You can purchase Yoast SEO Premium and receive our Premium email support and we can help you further.
