Stylelint config not adhered to

Having an issue, only recently started, where when I save a CSS file certain values are changed in what is the opposite of the stylelint config we have in the repo. Specifically it turns uppercase hex color values to lowercase. And in doing so my code fails the build because we require uppercase.

This is the relevant setting: 

'color-hex-case': 'upper',

I don't see anything in settings which would cause this either. In the code style > stylesheets > css I even have "Convert hex characters to" value set to uppercase!

Any help appreciated.