Alright, you put me on the right track, I found out what was going wrong:
I used WinSCP to upload the unzipped content. In WinSCP for my normal workflow I have a file transfer profile that omits everything with "scss" and "sass" and does not upload it. So the SCSS files never reached the server in the first place. *facepalm*
I now unzipped the archive directly on the server and everything works as it should.
So my bad, sorry for disturbing. ;)
Looking forward to explore Typesetter CMS!