The plugin does not work well

@lutiluc We’re sorry to hear you’re experiencing this issue. Can you please confirm you are using the most recent Yoast v15.5? You can learn more about updating here: https://kb.yoast.com/kb/how-can-i-update-my-free-plugin/

Also, can you confirm you are using WordPress 5.6? 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/
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If you have already confirmed that both Yoast SEO and WordPress are up to date and the issue is still occurring, we would next recommend performing a conflict check to determine whether another plugin or theme is interfering with the Yoast plugin. 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.