Thanks for the reply. I've tried restarting Spine, and reinstalling it, but it still has the problem. It is 3.7.780-beta. I found a workaround where I can load the image files from the hierarchy, and one by one drag the images to the set up. However if I load the .json file through Import Data, the set up screen is a flat grey, and if I create a new project from that point on, it'll continue to have that problem, where the workaround doesn't even work.
Is this problem in the essentials/pro versions?