Hi Marco, a while ago I was working on projects for Siemens Financial Services and I remember in some cases I had to use a workaround to log on to StudioPro. This was related to the browser (and maybe also to the fact that I was using a Virtual Client, but not entirely sure..)
The default browser was not able to use the redirect, so what I had to do is, when the websignin failed, copy the URL to a different browser and press enter. That way the signin completed successfully and the response was returned to StudioPro.
Hope this helps. If so, you may want to switch your default browser (if allowed by your company policy)
Apparently you are right, I tried with other browser and it works