Hi,
Thanks for purchasing Pro.
I can help out here.
I have not seen this happen before, if you try with a different browser does it unzip the file as well after being downloaed?
In most OS’s you can right click the folder and rezip it, do you see that option?
Otherwise you could use FTP and go through your hosting’s cpanel file manage and upload the folder there to the plugins directory.
We also have some notes here that might help:
Installing a WordPress Plugin
Let me know what you find out and we can go from here.
Thanks