Apple Photos (Mac) Can't Share Certain Photos

Hey

Running Apple Photos 5.0 (161.0.120) on Catalina 10.15.7. I have a few thousand Tiff photos from scanned prints that I share with family members via Photos, using a number of individual folders, e.g., "1980." I've been doing that for years.

Lately, when I create a new shared album and try to add photos, I get vague error messages, usually "There was an error adding the selected items to ‘1980.‘"

After running Onyx to no avail, countless reboots, making sure every last update is updated and repeatedly creating and deleting shared folders to get a different result with no change, I noticed that I CAN add SOME photos but not OTHERS and the photos that prompt the errors all seem to be those which have location info, i.e., photos that I used Apple Photos itself to "assign a location." The photos that have locations assigned - again, using only Apple Photos, cannot be added to shared folders while the photos without any location, can be added.