That Javascript error could have been caused by a conflict with another plugin and may not have been related to an error with the folder data that a reset would repair. The failure to load the user interface means that it is now encountering an error while loading the page. You can find out what the error is by turning on WordPress debugging.
To turn WordPress debugging on, edit the wp-config.php file and change
define('WP_DEBUG', false);
to
define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', false);
@ini_set('display_errors', 0);
(Be sure to change this back when you are done.)
This will allow different kinds of messages, some will not be related to Media Library Folders, will be written to a debug.log file in the wp-content folder. Now visit the Media Library Folders page and then check the debug.log file. If you find something, please send the debug.log to me at [email protected].
