Got a question:
is it also possible to have the arrangement in Song Mode to not play in a loop?
Maybe it’s obvious and I am just not seeing it. 
You mean that it doesn’t stop at the end of the song? If so - then no, it automatically restarts.
BUT you could add a pattern at the end with a Tempo Step FX to stop it.
Yes, that is what I meant.
You know why that is by default?
And does it do this weird thing at your end, that when it repeats that some
patterns sound differently as they should, not playing the pattern with the
correct instrument setinngs?
(I had the cut off set to half, it plays fine the first round, next round it’s ignored.
Have to stop the song and restart to correct this.)
Oldschool Tracker Behaviour. 
Was used very often for chiptunes and all other sorts of tracks.
Hm… i’ve never really paid attention past one play through. Do you have a example project where you can replicate that behaviour? Might be worth sharing as a bug report.