@c4m We’re sorry to hear you are experiencing this issue on your site.
Can you please let us know whether any particular action triggers the error message?
Also, can you confirm you are using WordPress 5.6.1? You can check by clicking on the W in the top left and selecting About. If you need to update, please check with your host provider. Please know that if you are using an older version of WordPress Core you may experience unexpected behavior with Yoast. This guide explains more: https://yoast.com/why-we-dont-support-old-wordpress-versions/
If after ensuring that both WordPress, Yoast SEO, and your other plugins and themes are up to date the issue is still occurring, we’d next recommend performing a conflicting check to see whether another plugin or theme is interfering with the Yoast SEO Plugin. This will help us narrow down the exact cause and determine what the next steps are while saving you time.
The fastest way to do this is to?deactivate all non-Yoast plugins and switch to a standard theme?like?Twenty Nineteen.?Test this on your development or staging site, if you have one. If not, we recommend using the?Health Check & Troubleshooting?plugin. This plugin allows you to run a conflict check?without affecting normal visitors to your site.
If you’re unfamiliar with checking for conflicts, we’d like to point you to a step-by-step guide that will walk you through the process:?How to check for plugin conflicts.
