I am attaching a zipped datapack which Minecraft can't see into.

If I unzip the pack, it works. If I re-zip the pack, the new zip works.

The original (attached) zip file was written using a program*. I am unclear if the program might be writing some invalid zip file (which Windows is still able to read, but Minecraft cannot), or if the file is a valid zip (and Minecraft is too strict about the types of zip files it can read).

• The program uses .NET System.IO.Compression.ZipArchive library to write the zip file, and each entry uses System.IO.Compression.CompressionLevel.NoCompression

EDIT

OOPS, the zip contains an entry where a file separator is '\' rather than '/'. Windows can read it, but it's an illegal zip file. This bug can be resolved.