I don't see anything obvious that would effect download from iCloud to your iMac. It sounds suspiciously as if there is a "damaged" file somewhere in the system. There are a few things you might try, but not necessarily in this sequence. My advice would be to read and understand all of the options before choosing your first course of action...
  1. Logic would seem to indicate the first image that failed to download has the highest probablility of being damaged so…
    1. Log onto iCloud > Photos and export the first image that did not download to your computer or your iCloud Drive
    2. Delete that image from iCloud Photos
    3. Cross your finger and hope the other images do download. 🤞
  2. Worth a try…
    1. In Photos > Preferences > iCloud > iCloud Photos change "Download originals to this Mac" to "Optimize Mac Storage"
    2. This will replace the images on your iMac with smaller imaged optimized for display on your iMac screen
    3. the full resolution images will be retained on iCloud but the difference will be invisible to you. If you Edit an image on your iMac it will be the full resolution image on iCloud that is changed as well as the optimized version on your iMac and your iPhone.
    4. The whole process will be invisible to you.
    5. This might allow the optimized image to be downloaded to your iMac instead of a damaged full size image
  3. Assuming you have a Time Machine backup:
    1. In Finder Select the folder /Users/yourid/Pictures
    2. CLick on the Time Machine icon on the menu bar
    3. Form the drop down menu select "Enter Time Machine"
    4. Using the Time line on the right side of the Time Machine window scroll back in time to a date when you know the Photos were downloading from iCloud correctly (NOTE: this may take several seconds but watch the date to the right of the Finder window)
    5. Select the Photos Library icon
    6. Click on Restore
    7. This will restore the Photos Library to a point in time that you know it was working. If the problem was a damaged database the new images should be downloaded from iCloud but it may take a few days.
  4. Or…
    1. Follow these instructions from OS X Daily to create a new Photos Library.

Last edited by joemikeb; 12/06/18 06:19 PM. Reason: #^A$% spell checker
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