Answer from other thread, (posted a community wiki).
Here's a solution that has been very reliable for me:
- Change the file extension of your .xlsx file to .zip
- Unzip this zip in a new folder
- List item Using Explorer, in that folder, search for the name in the file CONTENTS.
Note: Sometimes the name is written in URL format, e.g., %20 instead of spaces, so you might consider using a simplified string that is found only in the problematic file. I used last word of the filename + .xlsx.
It will probably return sheetN.xml as a result. This is the file corresponding to your problematic sheet, where N is the number of the problematic sheet in the order they are displayed. Open it in a text editor such as Notepad.
Find the search string and look at the code around it; it should point you to some cell references that you can lookup in the problematic sheet.
Note: As pointed out before, it could also be in Conditional Formatting or Data Validation.
Source: /719931/how-to-find-broken-links-in-excel-that-cant-be-broken-with-break-links/