Sierra Photos thumbnails missing I'm using Photos to organize my photos since it came out. However, since the Sierra upgrade, the thumbnails for many of my photos are showing as missing:



Most of the photos do not show properly when double-clicked, but going back and forth between the photo display and the photo editing tools seems to sometimes get them back.

This seems to happen indiscriminately with iPhone photos and Canon RAW photos. In addition, some thumbnails are purely associated with the wrong photos:



How can I make my thumbnails come back? Is there any risk of losing the photos themselves?
Try repairing your Photos library. You can do this by holding down the keys Command + Option when launching Photos.app.