File download via Zipdownloader tool creates damaged archives?

What steps does it take to reproduce the issue?

• go to any dataset using the standalone zipper tool (e.g. https://doi.org/10.11588/DATA/N1T5T8)
• press button "access dataset" -> Download ZIP
• try to extract the files in the ZIP

What happens?
The extraction of files from the zip fails:

unzip -v dataverse_files.zip

Archive: dataverse_files.zip
warning [dataverse_files.zip]: 10342 extra bytes at beginning or within zipfile (attempting to process anyway)

Apparently, each file has a bad zipfile offset.
We tested the multi file download for different datasets, on different machines, checked the Payara and Apache logs but found nothing obvious there. The single file download (= not using the zipper tool) works perfectly.

To whom does it occur (all users, curators, superusers)?
All users.

Which version of Dataverse are you using?
v 6.5

Any related open or closed issues to this bug report?
I found none.

Start by reproducing the standalone zipper download from the linked dataset and checking the resulting archive with unzip -v. Trace the multi-file download path used by the Zipdownloader tool, contrasting it with the working single-file download. Done means ZIP archives extract without offset warnings across multiple datasets, with regression coverage for the affected path.