How do I mark this issue as solved? After looking at way too many other issues, I’ve got convinced that the problem was in OTRS. And after digging for a while, I discovered the following on my Custom Fields in my OTRS 6 installation.
One of my dynamic fields had the name “Title” So my recommendation for somebody going the same route - if something is not importing as it should, look and look again at your dynamic fields!
Oh and another thing that helped me was to try also the import from the web interface (not only from the console)
Please feel free to mark this ticket as “SOLVED”
Happy and ready to go into zammad deeper today 
Adrian