I'm not sure if there is some sort of limit to how many pictures or videos can be uploaded. I created a folder for the Pregnancy and Breeding group I created on this site so I can have the pictures linked directly from the folder, instead of linking to other sites.
I can select the stills and GIFs, and they upload just fine showing the green checkmark to indicate success. But days, even weeks later, the pictures still don't show up in any of my media galleries, let alone the one I selected prior to uploading.