SP7 pen and touch movement not smooth but wavy?

https://i.imgur.com/S5Sfhdn.png

Some example lines. I drew the left set with the same pen, on my old SP3. But on the SP7 they are very wavy. I've also noticed this waviness when using finger input and moving windows diagonally. Vertical and horizontal are pretty smooth, as I approach 45 degrees it gets progressively worse.

This is the type of pen I'm using, if it matters: https://i.imgur.com/dmPoFYy.jpg

Is my SP7 defective? Should I return it?

Edit: Picked up the newest pen model, wavy lines are basically enirely gone.