Hey, same issue here today trying to use the modding tools for KCD2.
When i download manually and just drag the .pak into my MODS folder. The mod works, if I unpack it through winrar then repack it through winrar (as a zip that I later rename to .pak) it will crash saying it is corrupted.
I havn't even changed any content of the xml files within the .pak
Have you had any luck finding the issue ?
Cheers