Get rid of unknown links

I have some large files that I inherited that are causing a lot of problems, so for 2017, I built a new file. Somehow, when I copied something from the old file to the new one, a link was created to a file that doesn't exist. I've tried inserting a new worksheet then deleted all the other worksheets, and the link still exists. I've tried breaking the link, but it still shows up as a linked file.

No formulas, no named ranges, no conditional formatting, no hidden worksheets. I've tried everything I could find online.

How can I get rid of this???

Added a sample file. You may note that the file size is way bigger than it should be for that small amount of data, so there is something in the background that I can't find.

Thanks,
David