Please try the following steps:

  1. Go to the Tag Groups Settings, submenu Troubleshooting and there to the First Aid tab. Click all buttons from top to bottom and then check if the problem is solved.
  2. Check the "logical operator" (in the shortcode it is the parameter "operator") and try a different logical condition.
  3. If you use the Meta Box for tags: Open one of the posts that don't show and check if the tags you used have been used in the correct groups.