Welcome to Tom's Hardware, @enochered!
This sounds pretty unfortunate. However, I think that you might be dealing with a permissions issue on your Mac. I'd strongly recommend you go to Disk Utility and
Test the external HDD for defects from there. When you got 'First Aid', you will see the option to 'Repair Disk Permissions'. Hopefully, that would resolve your issue.
EDIT: Have you had any recent updates on the Mac and have used this particular external drive on other operating systems (Windows OS)? If this is an NTFS-formatted drive and you use a third-party tools to read the files from it on the Mac, maybe you should check if you have updated the software as well.
Let me know how it goes.

SuperSoph_WD