Importing .xlsx files

I am having a strange issue with SPSS 27, when importing some Excel-files that I created with Mathematica 12.1. The files open without problems with Excel but when I try to import them into SPSS the checked box to get the variable names from the Excel files becomes unchecked and no data are read. If I just read the Excel file and Save as under a new name, SPSS can read the new file.
I cannot see any difference between the Excel files except that my name appears under "Last saved by:" in the new file. Is there a way of reading the original files without opening in Excel and "Save as" each of them?
It would be great, considering that I have over thousand files that would need to be "converted" if there is no other solution.

Any suggestions on how to handle this issue would be greatly appreciated!