Can't get the drag and drop to work

[Kristoffer Midttømme]

This looks like a super useful tool for me, but I can't get the drag and drop to work. I have created a project with two parts, but cannot seem to drag any posts from the left-hand side to the parts. I can drag the post(s) but there's no dashed box for me to drop them in, like the ones I've seen in youtube screenshots. Am I doing something wrong? I am on wordpress 4.7.1