I can confirm that the zip files are indeed corrupted or rather being sent in an unsupported format. This is definitely an issue with the server so the first thing I would do is to check if the latest ziparchive module is installed on your server and then try again.
You can consult with your hosting provider for further checks on the ziparchive module.
My apologies for not responding sooner. I'm still not sure what is causing this issue, however I do suspect that the site might be corrupted in some way that is producing the faulty zip files for our Toolset plugins.
Is it a cause where you're moving your entire site or just moving over the Toolset data structure?
I might possibly need to escalate this one to our 2nd tier supporters for further debugging.
Also can you let me know when did you first notice the issue ?