Because of Windows interfering with connected interfaces, it showed the owner a message to reset things.
Bam! - fixed installation config down - no more light.
Resolving the issue by facebook, then more direct thru messenger, via teamviewer and phone, 90 (!) minutes later the issue was solved.
<TL;DR> Windows putted itself somewhere and I configured the wrong IP-network based on info available at that time...
If only there would have been a little sticker telling me on what network we were looking for! Please?
Mark your stuff! (twice)