Photos.app not downloading image contents Photos.app has been working fine for me since its release, but more recently, photos taken on my iPhone and added to my Photo Stream were not appearing. An empty rectangle would show up for each new photo, and the rectangle would be sized appropriately (portrait/landscape/pano), and they appear grouped by location, but there isn't actually any image content. No thumbnail, and clicking on the image opens up a blank screen. The settings dialog says its trying to download, but the progress bar never moves.

In trying to fix this, I deleted ~/Pictures/Photos Library.photoslibrary entirely and created a new system library. Now all of my photos are in this state, not just the new ones. This persists across restarts of the application and the entire system.

I trust they're still up in the cloud someplace... they're on my iPhone ok. But I'd love to figure out why they won't show up on the desktop. 

See screenshot for the current situation.
Updating to 10.11.4 fixed it for me.