Sometimes you may experience that filters on the front or back end don’t show all posts. You can mostly fix it with the “Migrate” button in the Settings: Search in the “Troubleshooting” section under the “First Aid” tab.
The Tag Groups Premium plugin adds further information to tags and posts and tracks any changes to them, if necessary. When you activate the plugin, tags and posts are migrated automatically. Since no existing data was removed or changed, your posts and tags still work with other plugins and themes, and even after removing Tag Groups Premium everything will be functional, although without the additional features.
If you or a plugin makes changes that could not be tracked (for example while Tag Groups Premium was deactivated, if you imported posts or if a plugin makes changes to the database directly), this additional information is out of sync.