Hello @spiro and welcome to the forum 
Without knowing exactly what you’ve done, it’s difficult to figure out what may have gone wrong. So, please answer some questions:
It looks like this involves the ‘Sketch V2’ brush bundle from here?:
Sketch V2. (SK2) Pleasure to draw. including colored pencils and blenders
Did you use this download link:?
https://files.kde.org/krita/extras/Sketch%20V2%20for%20KRITA5.zip
I’m guessing this. So please tell me if my guess is correct.