@Moritz_Bunkus: What I find quite disturbing as of yet is still though that there seems to be close to 0 from Univention directly and by the mere number of posts regarding this special topic I think there really should be at least some sort of reaction. While it is true that samba made this changes I personally would have expected a bit more QA or at least reaction in this topic. Not wanting to rant at all, I know a lot of Univention guys and they’re really great (I mean it with every word) I still find it a bit disturbing nothing happens in these cases for weeks now. 
… Well, whatever it be: Let’s hope they’ll find a solution to these problems as well.
ref: UCS 4.3 Samba 4.7 - Probleme beim Authentizieren (war: Änderungen bei NTLM?)
ref: Windows Fileserveranmeldung nach UCS Update auf 4.3 nicht möglich
I’m just happy I could at least solve my issues by the solutions I’ve posted. Wish you good luck alltogether!