The same thing happened to me as well and I actually realized it just now after I stumbled upon this post.
I uploaded the first version of my game directly to itch.io and everything worked as expected. Later, I uploaded a new version (an APK file as well) with butler and I didn't notice that it was actually uploaded as a ZIP file. None of the people who downloaded the Android version mentioned that it didn't work. I had obviously already tested the APK before uploading it so it didn't occur to me to test downloading it. Sigh. Very annoying to realize this so late :D
I just tested downloading the ZIP file and it shows up as an APK file on my Android phone which is a bit weird. However, when I try to open the game, it says "There was a problem while parsing the package."
I reuploaded the APK files directly to itch.io now. Hopefully you'll be able to fix this sometime soon!
I have butler version 15.21.0 and I'm on Windows
Edit: I tested pushing a PNG file with butler and at first it showed up as a ZIP but later it changed into a PNG. I'm confused.
For me it's confusing that a normal upload works.
I'm a web dev myself and I normally would use the same API for uploading from my page as I would use for other services. So it should work.
Plus a fix to this problem should normally be a matter of a few hours. It's just like (if data ends with *.apk than don't do your packaging stuff)
