I used to see this error
- when excel has formulas with functions like Today(), Now(). When such excels are opened and closed there will be a pop up that asks for saving the changes
- when office activation message pop up
- when there are any links (urls/links to other workbooks) that request for update/refresh before closing
You can check this by manually opening and closing excels that gave the error.
workaround for point 1
open excel → File → Options → Formulas → Calculation options Select Manual and uncheck Recalculate before saving
workaround for point 2
activate your MS Office or we can handle the pop up message as an exception
workaround for point 3
Check for any connections/links and break them. You can check this under Data tab “Existing Connections”
hope this helped