It makes me think that Xojo maybe is building a non-compatible zip file envelope structure to hold the compressed streams. So only FolderItem.Unzip could expand such “zip” file.
Edit:
I’ve made an experiment under windows and I could see the files from a folder I’ve zipped.
No exceptions thrown, but “LastErrorCode” was 101 that maybe is not a real error.
The bug seems present in other places too: folderitem.lasterrorcode after copyfileto has 101 and should be 0