Hi @ Wataru Kitagawa
Since your file is written by code, I can't do the test, thanks for your understanding.
But based on my past experience, usually, if Excel file was generated by third-party tool or code which may generate quite limited XML scheme.
Although, this XML scheme is enough to open the file in Excel, but not enough for some specified Excel features, such as Spreadsheet Compare.
Here is a thread with the same error message: Specified part does not exist in the package.
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