yarn offline directory inaccessible, upon use of --offline get an error of "UNKNOWN error, mkdir" even though the offline directory in question exists

[VKRM94]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?
I setup the yarn offline cache as instructed by the yarn blog post. My yarn offline directory also has all the offline packages. But when I delete the node-modules and LOCK file, cut off the internet and run yarn install --offline I get an error:
An unexpected error occurred: "UNKNOWN: unknown error, mkdir '\\vkrishnan\\yarnOffline1'".

If the current behavior is a bug, please provide the steps to reproduce.

What is the expected behavior?
This error only popped up a few days back. Earlier my yarn offline cache was working as expected with me being able to use the offline cache from a machine on a network.

Please mention your node.js, yarn and operating system version.
$ node -v
v8.12.0
$ yarn -v
1.12.3