Sierra Photos thumbnails missing

Question

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?

Answer 1

Try repairing your Photos library. You can do this by holding down the keys Command + Option when launching Photos.app.

Answer 2

This may be a possible solution:

1. Open your Photos App
2. Click on Photos (in sidebar on the left)
3. Select one thumbnail and then press Command+a, in order to select all photos at once
4. After having selected all photos, right click, and click on Rotate.
5. This will take a while depending on the amount of photos you have.
6. After it has rotated all the photos, select all the photos again, and click on Rotate anti-clockwise, (to get the thumbnails rotated back to normal)
7. This should solve your issue!! i.e. this is a workaround to rebuilt your thumbnails.

Note

Do not use cleanup software such as CleanMyMac, especially not for Photos at least. This is the most probable cause to destroying the thumbnails.