I think I can clarify a bit more. The bug is also present when aiming at a shot projectile. When no projectile is present aiming behaves just as it should. But, when a projectile is shot in the sand and you are aiming directly at the projectile the mouse sensitivity suddenly jumps up drastically.
Although the mouse and settings will most likely not be the problem as it is reacting to an ingame object which is not accessible from the mouse:
Input settings:
MouseSmoothness: 0,
MouseSensitivity: 0.063662,
DPI: 1500
Logitech g502
There are multiple reports of this problem, e.g.:
I think people are referring to: Aiming at animals, that the problem mostly occurs when you aim at an animal with a projectile already in it. You are actually aiming in the direction of the projectile. This is why people think it is the animal, but in my opinion it is fact the already shot projectile stuck in the animal.