When you are uploading images into Wordpress, you may experience a technical issue wherein the images appear as light gray tiles in your Media Library.
If this happens, it is usually because you have uploaded too many images at once. How many images you can send in a single upload is limited by the speed of your internet connection.
To correct this issue, upload one image at a time. Wait until the image changes from a light gray box to a thumbnail. This means the upload is complete.
Once that upload is complete, you can upload another image.
If you do not want to upload one image at a time, try uploading smaller batches. Start with 3 and work up from there until you know the limit for uploading multiple images at once that works with your current internet access.