Please try the following steps:
- 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.
- Check the "logical operator" (in the shortcode it is the parameter "operator") and try a different logical condition.
- 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.