Hey Rider!
The first message is simply a warning (and actually, Windows doesn't seem to support mode 0600, so I should fix that).
As for the second message, it looks like this issue: https://github.com/itchio/butler/issues/62 - are you pushing a zip file? Can you try pushing a folder directly (without compressing it to .zip first) and see if it works? I'll try to fix that issue soon anyway.