It seems to depend on the game speed or fps speed.
If your fps drops, then your view speed drops too, this means if you have like for a really short time no refreshed frame, then you stuck with your view and the game won't take any input from your mouse for that time.
That's why you need to move your mouse for a longer time as you would if you had high fluent fps.

I just noticed that anything is juddering when i look at it, it doesnt't matter if with scope or not.
With zooming in you can see it better.
It's very distracting when you try to look through a wire fence, or lying down at the grass and its jumping at the screen.

Yeah I'm sorry! I'm not that good at english grammar (not my native).