dragging photo from photos app to desktop says "missing file"

In recent months I've had an issue with some of the photos in my photos app.

When I try to drag the photo into an email or other location it says the original file is missing.

I don't know why that is happening.

Some photos we have (this is a business) are from our installers phones, being sent to the iMac via bluetooth.

I always make sure the transfers are completed before letting them walk away with the phone.Could the bluetooth transfer have anything to do with it?

I've never had this issue before.