Shared album photos appear as gray box
I uploaded some photos to a shared album and my friends say that some (not all) of the photos don’t appear in the album. Instead, they show up as a gray box with a cloud logo in the lower right hand corner. When they tap the photo, the cloud turns into a moving timer icon but gets stuck 1/4 of the way. Why is this happening and what can I do to fix it?
iPhone X