@rizaardiyanto Worked for me also!
I installed plugin to local copy. I could see the sidebar widget on posts. I went to Settings and enabled it to custom post type and the i changed date&time setting to d.m.Y and H:i. After saving settings the widget is not visible anymore on the posts sidebar.
I’m having the similar issue. Metabox is not visible on posts, pages or custom post type. There are no errors on the javascript console. There seems to be few similar post during last couple of weeks.
