Apparently there is a limit in place which prevents you from uploading more than 1 image to a project per minute. This makes it even more tedious to update all images for one of your projects, as you will now have to sit and wait one minute between each upload.
Any chance you can either lower or remove this limit completely?
I'm not sure what's going on here; I checked the settings and the time limits are turned off for Project Authors, so I looked at your user profile and see that you are indeed classified as one. I'll ask the devs to look into it.