Copy the contents of the spreadsheet to a new one, and deleted the old one (it wasn't a particularly important spreadsheet, thankfully), and everything was fine.
If you need to move a source link into a Spreadsheets, first set up your spreadsheet.
After your spreadsheets are set up, copy values from the spreadsheet into the workbook and then, in the clipboard that appears after pasting the values, choose to move source links and confirm your choice.
If you are moving a large number of source links, you should share after every 100 links moved.
Source links cannot be moved from a spreadsheet to a workbook, or from one location in a spreadsheet to another.
I’ll end with some recommendations of when each method should be used.