I had this issue after migrating from local development to a Media Temple Grid server. @JonathanSoper’s fix worked for me (Thanks, Jonathan).
EDIT: I also had to modify ‘core/fields/wysiwyg.php’. I changed this line:
$plugins['code'] = apply_filters('acf/get_info', 'dir') . 'js/tinymce.code.min.js';
to this:
$plugins['code'] = get_bloginfo('url') . '/wp-content/plugins/advanced-custom-fields/js/tinymce.code.min.js';
But editing plugin files is less than ideal. Any chance we might see a fix for this at some point, @Elliot Condon?
Thanks!