There is a regression in the last Ionic.Zip binaries, when I zip a folder that contains files which contains not standard characters then it produce wrong zip files.
I use :
zip.AlternateEncoding = System.Text.Encoding.Unicode;
zip.AlternateEncodingUsage = Ionic.Zip.ZipOption.AsNecessary;
It works with version 22.214.171.124 with :
zip.UseUnicodeAsNecessary = true;
You can try with a folder name that contains a "È".
I'm also sad to see that this library is a bit dead :(