Taxonomy term doesn't show up in admin/structure/taxonomy/manage/tags/overview I migrated a Drupal 6 site to Drupal 8.  Current running version is:  8.5.3
I created 4 terms in the Tag taxonomy and referenced in the content type Article.

The terms, however, do not show up in the overview page.


  


They are in the database.


  


They are also visible when creating nodes.


  


How do I fix this?
It sounds like they are missing parent value of 0 in the term hierarchy table. That will do it. That table just needs the tid and parent value of '0'. Try it by adding one of the tag term tids to that table, clear the cache and reload that page. This is easy to miss in migrations.