Ok. I found the fix to my problem. See below quote.
For Mac Users, it bears repeating:
“I just found out that Safari automatically unzips files, and just shows the unzipped folder (the original zip-filed is automatically trashed). This is an option that can be switched off in Safari -> preferences -> open ‘safe’files. If unchecked, zip-files download just fine and remain zip-files (and thus can be ‘seen’ by WordPress).”