What I think is happening is that the "apparent size culling" is culling the character's head mesh as a separate entity from the body, and since the head is much, much smaller, you'll see the head get culled based on it's size much sooner than the body, leading to this weird "headless" appearance. And, size apparent size culling doesn't appear to take into account FOV (i.e. using a scope) it can be very obvious.
Video on Streamable
What I think is happening is that the "apparent size culling" is culling the character's head mesh as a separate entity from the body, and since the head is much, much smaller, you'll see the head get culled based on it's size much sooner than the body, leading to this weird "headless" appearance. And, size apparent size culling doesn't appear to take into account FOV (i.e. using a scope) it can be very obvious.