Yoast SEO plugin manual installs failing

I’ve downloaded and unzipped the files, and transferred the folder to /wp-content/plugins via SFTP. No errors occured, but logging into /wp-admin they don’t show up under the list of installed plugins, so I can’t activate them.

All the permissions are 775, the files aren’t nested inside another sub directory or anything, and I’m able to delete and reinstall existing plugins in this way with no trouble.

How to proceed?

similar problems with wordpress meta robots