I have been using Cygwin for many years, although I wouldn't call myself an
advanced user.

I'm working with some much newer users.  They set up Cygwin, but I didn't
see them do it. I ran "uname -a" and it was about the same as mine.  I
compared the output of "env|sort" and I saw some differences, but I can't
tell if they were significant.

When I run the following command:

    kubectl config use-context dev2ff

It works perfectly fine, setting the correct context.  When this user I'm
working with runs the same command, he gets this (replacing his userid with
"..."):

    error: FindFirstFile C:\cygwin64\home\.../.kube/config: The directory
name is invalid.

He did have "HOME=/c/Users/...", but I had him change it to "/home/...",
but that didn't make any difference.

I'm not sure what could be happening here.