Harmonic minor is correct.
The difference between the two (harmonic and melodic minor) is that the human voice does not like to sing the same scale minors coming down as it does going up. It’s a (mostly) physical limitation of the human voicebox.
That’s why songs change key. Thus strictly speaking the melodic minor doesn’t exist (yes, I know it does) on it’s own but only accompanies the harmonic minor for practical purposes as outlined above. although the blues scale minor, being the same going both ways, does.
Nothing to do with Cubase really.
I don’t know what you mean by the “Once you open and close the plugin… it’s ok.” Lost me on that one.