I see you're on IIS (kudos for the bravery on hosting with IIS). Make sure the PHP module "fileinfo" is loaded in your configuration. If it's not, it's the reason why the upload never actually happens.

As mentioned on GitHub issues, it's probably related to old accompanying libs for fileinfo or to wrong MIME detection. In any case, let's continue this over at GitHub in case it requires a change in K2.

You're welcome :)