Proxy models (Such as Weapon Flashlights, Night Vision Goggles, Optics/Scopes, Suppressors, Magazines etc.) that can be attached to the character and the character's weapon, experience slight jittering or micro-teleportation's. It seems to me, this bug is only prevalent when a proxy model (such as a helmet or weapon) which is attached to the character, has another proxy model attached to it, causing some form of lag or unsmooth animation.

The M4A1 is a good example to showcase the prevalence of this bug because the weapon itself is the most modular in terms of attachments.