The list on the Tag Groups page doesn’t load. I only see the wheel spinning forever

This usually means that somewhere your blog outputs a warning or alert that interferes with the data transfer to your browser. In most cases it is caused by another plugin.

Try the following:

  1. Deactivate all other plugins and switch to a default theme. Then run the test again. If now all seems OK, re-activate them one by one (and keep running the test) to identify the one where it breaks.
  2. Add to your wp-config.php file the following lines:

    define( 'WP_DEBUG', true );
    define( 'WP_DEBUG_LOG', true );

    Then run the test again and afterwards check the content of the debug.log file in the wp-content folder if there is any error message.
  3. Open the JavaScript Console in your browser and check the error or log messages for anything that gives a hint about the cause.