No ZIP file written on some machines on Windows 10

I use Chilkat ZIP on VC++ for a software application that's run for years.

Suddenly, some users are reporting that the ZIP file isn't being written at all on their computers. On other computers (like mine), it's fine. I'm guessing (!) it has to do with a Microsoft Windows 10 update or a Microsoft support library changing or being missing.

1. Are there any similar reports?
2. Any ideas on what the problem is?
3. How do I debug it on someone else's computer? Report some error code?
4. I have a 2010 version. It looks like the latest is 2013. Would it pay to upgrade?
5. If so, how do I do that and how much would it cost?