The Search Engine Metainfo Dashboard is a table that allows you to set and override with custom and specific metainfo each links contained in the sitemap of your site.
Each record is associated uniquely to a link URL.
If you previously entered some values for the Metainfo records and now they don't show up anymore, it probably means that you are logging in backend with a different domain/www prefix.
Metainfo are associated to each link, if links change metainfo change too.
If you specify metainfo for http://www.mysite.com/ and open http://mysite.com/ without www prefix they won't apply, it's a different link. Most importantly, if your website is accessible with doubled domains http://www.mysite.com/ and http://mysite.com/ stop to do this immediately. It's a very bad practice for SEO, so consider to setup a htaccess rewrite/redirect rule to the preferred domain matching the one set in your Google Search Console.
The same happens if you had links without SEF rewriting http://www.mysite.com/index.php/mypage.html and change them to http://www.mysite.com/mypage.html activating the Joomla SEF rewriting.
The same happens if you change links for https starting with http://www.mysite.com/index.php/mypage.html and change them to https://www.mysite.com/mypage.html
Every time a link changes the meta data associations is lost. Keep in mind that the URL is the unique identifier for meta data that you entered.
If you are migrating a website from one domain to another, refer to this FAQ for Metainfo migration strategy: