Strokes disappearing with Apple Pencil

Lines disappear after drawing.

Here you see it in notes app but it's the same in other apps like pro create

1 https://vimeo.com/166409701

I think it has something to do with the palm rejection function. It seems to be flawed. I don't lift my palm during writing or drawing but the behavior is as if I had lifted the palm of the writing hand and put it down again.

If you start without having your palm rest on the display and put it down while still drawing the line disappears every time.

2 https://vimeo.com/166433606

Is this the same with all iPad Pro 12.9 devices and Apple Pencils — or is it just my iPad?