Wanhao duplicator i3 - 5th layer not sticking

Hi,

I have an issue with my new duplicator i3, 1.75mm Filament, mk10 extruder. I use simplify 3d, I tried 0,1 and 0,2mm layers. phenomenom is the same.
I use skirt, raft and ooze shield. I tried temperatures from 190 - 210 °C its always the similar problem.

So far I managed to set the heigth of the printing platform using the 4 screws.
However - when I print - the first few layers print OK and stick nicely to the platform - but then the first solid layer doesnt stick to the raft at 1 or two corners.

Is this a setting issue or a hardware problem - does anyone have a checklist howto see what is the reason?