Unfortunately I think I’m having the same problem on my site :https://www.rachelgreisman.com/#!/editorial/
At one point all my NGG’s were working just fine. I don’t recall if them not working started with an upgrade or what….but now when I click thumbs I just get a blank slate. The weird part is I had tried completely uninstalling NG and reinstalling, reuploading all images, etc. The first time I previewed my site the gallery worked fine! But then when I refreshed it has since stopped working.
Keep me posted if you find a solution here. Haven’t checked file permissions as you mentioned above…where do you find that?