Not compatible with object caching on back-end (like WP Engine)

Hey Jeffrey,
I just wanted to give you a heads up that this plugin won’t work correctly with some web hosts, like WP Engine, that perform object caching on the back-end. I was convinced that the bulk category feature was broken until I realized that the results were being cached.

For users of WP Engine, try adding something like this to your functions.php

add_action( 'load-upload.php', 'clear_category_cache', 99);
function clear_category_cache() {
  wp_cache_flush();
}

Cheers,
Dalton

https://www.ads-software.com/plugins/wp-media-library-categories/