This release of the free Tag Groups WordPress plugin comes with two new features: List your tags in columns under their respective group names or under their first letters.
Alphabetical Tag Index 
Tag List
Read more in the documentation and make sure to check out the demos.
You will also find a new “First Aid” section in the “Troubleshooting” submenu. Two buttons will launch automatic routines that can fix common problems.
Term Meta – the Technical Part
Since the beginning of the plugin, we were using the term_group field in the database table of tags (or, more generally, “terms”). When ever the plugin was upgraded to the premium version, we had to migrate this data into another place in the database (in the “term meta”). That is because the premium plugin needs to store an array of group IDs, rather than only one integer.
Term meta is only available since WordPress 4.4. Recently the minimum requirements of the WordPress version was raised to 4.9. Raising the minimum requirements made it not only easier to test new releases, but also to use “term meta” throughout the plugin.
The transition from the free to the premium version is now much easier. We additionally can benefit from better performance for some operations.
This mandatory migration happens in the background. If something seems wrong, you could first try the “First Aid” buttons on the “Troubleshooting” page.