[yamcenutzer]

Kodi doesn't support Active Directory.

True in that Kodi or LibreELEC can't be a member of a domain, but there are zero issues connecting to a domain member machine. I've been doing it for years, the problem is that Kodi has been lagging way behind with SAMBA and it wasn't until the recent issues where everyone is now being forced to abandon SMBv1 that something is finally getting done. I have threads and reports on this going back a few years asking for proper SMBv2 onward support.

My recommendation, as it's what I did with my Window 2016 domaim media file server (was 2012 until last week), is first disable SMBv1 to get that out of the equation, then try again with any of Milhouse's recent builds. It now attempts to connect all the way up to SMBv3 and you can use the GUI to add the sources as SMB, specifying the username as domain\account and the password. What you cannot do is browse for shares as that was SMBv1 only, you need to know the server name and the sharename and type them in manually.

That were my thoughts, I never expected libreelec to be able to actually join the domain (although I do that for some of my regular linux boxes)

Unfortunately, although I already had the media source in sources.xml and also can re-add it the same way, It simply does not work. It might be that, the media library on the sql server ist using some incompatible (older) version of the file feed, I don't know.
I just found the return message on the command line funny, since I don't see that when I try to connect with, e.g. a stock ubuntu 16 . The latter, of course has a non alpha samba 4.4 or 4.6.
Out of curiosity, what was the compelling reason to use a alpha/beta Samba instead of, say, 4.6?

currently with no nas access and pvr broken, it is pretty much unusable for me.
When I find time (weekend?) I'll try installing from scratch.