I've just tried to upload a thumbnail image to a category, when pressing save, the washed-out loading screen appears and never goes away. If I back out of that page and then try and go back, the loading screen is still there. Logging out, quitting the browsers doesn't seem to make any difference. The category is now uneditable in the admin.
This was a migrated site, and first time I've checked thumbnails - the rest of the migration was perfect.
This is the exact issue, but no answers... Uncaught TypeError: value.map is not a function coming from file-uploader.js Please help!