The Yoast SEO update has moved the meta description. It used to be at the bottom of the YOAST SEO form on the edit post page, but it is now at the top under the SEO Title.
On November 18, Yoast released Yoast SEO 3.0. A couple of notes if you have issues from Yoast.
Please read the release post and see the video in it, specifically when you don’t know where to edit titles and descriptions.
If you are having issues with functionality not working on your edit post / edit page screen, please clear your browser cache before trying anything else. This has resolved 90% of issues so far!
If you have CloudFlare or Sucuri or another cache in front of your site, clear that cache too!