SecurityError-tinymce not working

I get this error when I want to insert the shortcode. How to fix?

SecurityError: Failed to read the 'contentDocument' property from 'HTMLIFrameElement': Blocked a frame with origin "/" from accessing a cross-origin frame.
 /wp-content/plugins/feedzy-rss-feeds/js/feedzy-rss-feeds-ui-mce.js?wp-mce-4403-20160901:56:22 insertShortcode()
 /wp-content/plugins/feedzy-rss-feeds/js/feedzy-rss-feeds-ui-mce.js?wp-mce-4403-20160901:41:9 t.onclick()
 /wp-includes/js/tinymce/tinymce.min.js?ver=4403-20160901:8:14427 t.i [as fire]()
 /wp-includes/js/tinymce/tinymce.min.js?ver=4403-20160901:8:30563 t.fire()
 /wp-includes/js/tinymce/tinymce.min.js?ver=4403-20160901:8:25384 HTMLDivElement.t()
 /wp-includes/js/tinymce/tinymce.min.js?ver=4403-20160901:2:12478 e()
 /wp-includes/js/tinymce/tinymce.min.js?ver=4403-20160901:2:12818 HTMLDivElement.m()