I’m also having this issue:
http://i.imgur.com/DVXm48n.jpg
I tried the suggestions in this thread (updating to 2.4.2, removing theme overrides), but no luck so far.
Switching to a different theme fixes the problem, so it’s definitely a theme conflict. I just can’t figure out what the root cause is, since there aren’t any error messages.
Also happening for me. Rolled back to the previous backup point.
I just ran into this issue, and fixed it by making sure the Initial Width and Initial Height weren’t blank. You can set these values under Primary Lightbox Settings > Size tab. I set both values to 10%, and the problem went away.
