I can only speculate that your email script is sending the link before the file is completely written, but the fact that it has all the content makes me think that is unlikely. Maybe you are using an older version of Excel::Writer::XLSX and it has been since fixed? (The change log does not indicate anything, though, and the git log has the most recent changes to the close() method at eight years ago).

You also say you use scripts, which suggests you are calling them using system, exec or similar instead of loading code from .pm files. Maybe there is something in that.

It is easier to diagnose issues if you provide a short, self contained, correct example.