When scrolling up & down with thumbnails shown, it's very obvious that it's loading the cover photos, even when you scroll down and immediately scroll back up to where you were just viewing. It's a visual distraction and takes away from the polished feel.

Seems that as soon as an image scrolls off out of view, it is released from memory.

Recommend loading the thumbnails for at least a page above & below what's currently visible and not releasing the photo from memory until it leaves that boundary.