photo file export errors

7.87 GB free on Mac

That is not enough. Try to free more storage on your Mac. I am trying to keep at least 10GB free at all times for the operating system to use and to have storage to download or save files.

But also check, if iCloud Photo Library is still enabled in System Preferences > iCloud. Sometimes this can get disabled and cause problems.

So the problem is not exporting at all but you seem to be using iCloud Photo Library and Photos cannot download the original from iCloud.

• Are you running low on storage on your Mac? The reason could be that Photos has no free storage to store the photo.
• If you are running out of iCloud Storage, iCloud will no longer work reliably, until you free storage in iCloud.
• A very common problem with the access to iCloud is, that you need to be connected to Wi-Fi (not a cellular connection) and some VPN connections, firewalls, and Antivirus software like Kaperski or Little Snitch may be blocking the connection to the iCloud Servers, i.e, if you are running macOS 10.13 High Sierra.

Which version of MacOS X is running on your Mac?

See this Get help with the Photos app on your Mac - Apple Support

FILENAMES ERRORS: "Could not load image"

What is the filename of the image in question? Is there something special about this filename? Does it contain special characters? is it possible to edit the photo?

Which file naming preset are you using when exporting the image? Is it "Filename: Use Title", or original filename?

And what about the free storage on your Mac or in iCloud? Do you have any third party security software installed?