It also the same problem if I follow the test procedure on my Linux desktop, take the zip file on a thumb drive, and try to open it in Windows.
If I take that zip file that doesn't work in Windows, unzip it in Linux, and then re-zip it in Linux so that I have a new zip file with exactly the same contents, *that* one works in Windows.
So it's something in the format of our zip files for zips of the top-level file directory, as we generate them in PHP. I ran "zip -T" on one of these, and it didn't detect any problems.
It also the same problem if I follow the test procedure on my Linux desktop, take the zip file on a thumb drive, and try to open it in Windows.
If I take that zip file that doesn't work in Windows, unzip it in Linux, and then re-zip it in Linux so that I have a new zip file with exactly the same contents, *that* one works in Windows.
So it's something in the format of our zip files for zips of the top-level file directory, as we generate them in PHP. I ran "zip -T" on one of these, and it didn't detect any problems.