Cannot Start Editing, Photos cannot load edits for this image

1. Check the image file if it’s imported ensure it’s not corrupted and make sure you’ve saved it to your photos.
2. See if you can open it with Preview or a third party image editor app
3. Quit photos and reopen, force photos to quit Command Opt and ESC keys together.
4. photo library may need to be repaired holding down option key and the command key click on photos and open the app. A box should appear asking if you want to repair select repair
5. Check your iCloud syncing maybe it is still syncing to the cloud or downloading to the Mac.
6. Make sure Mac is up to date
7. Export and reimport the photo. Delete the photo and reimport it.
8. Check storage
9. Check file permissions to ensure editing is permitted.

Hope this helps!!!

What app are you using you using to edit your photos? You did not mention this critical piece of information.

I will assume you are using the Photos app and these are photos you likely edited on another version of Photos. So for each photo that is causing the problem please do the following:

1. Go to "IMAGE" in upper menu.
2. Select, "REVERT TO ORIGINAL".
3. Next try editing.

You can also select the photos giving you problems in batches, export them and then re-import them.