This has been confirmed by Microsoft Support as a known XML Spreadsheet 2003 limitation: with this format there is a maximum defined of 65530 hyperlinks.
Export to Excel with hyperlinks is hitting 65530-links XML Spreadsheet 2003 limitation, throwing Unknown error when opening the xls
Steps to Reproduce:
Expected Result: Having the file saved and open successfully.
Actual Result: The saved file doesn't open, giving Unknown error message when loading.
Remove hyperlinks from some column(s) in order to get less than 65530 hyperlinks in the export.
This issue is documented as CLRT-61890, affects Clarity 12.0, 12.1, 13.0 and is currently under Development's review.
CLRT-61890 is marked as a duplicate to CLRT-65085.
For more information on similar symptoms, reference TEC561736: Unable to open Excel file after Export to Excel (Data Only) when the number of records greater than 3000 rows in Weekly Detail portlet.
Keywords: CLARITYKB, CLRT-61890, clarity12resolved, clarity13resolved, clarity1310resolved, CLRT-65085.