I've noticed several plugins don't seem to work. Some of these plugins are those provided in the official documentation (see list below), so it seems like a serious issue.

The non-working plugins appear under YOURSITE.com/admin/config/content/ckeditor/edit/Full
under EDITOR APPEARANCE > Plugins.

However, they do not appear under available toolbars, so I cannot add them.

Here are examples of the plugins that have an issue: