Same issue here. What a disaster. Trying to get our app in review for 43 hours now! Images are being randomly greyed. When you delete the placeholder and upload with drag and drop in Safari a renamed png image. First it looks like it uploads well and the after hitting the add for review button the same frustrating message pops up again and seemingly random images in localisations are greyed out. I am getting nuts! Apple help us out here! This costs loads of money, time and energy.