In case others see this, it’s likely due to how the FBBIK bones are set and weighted. This character is rotating the wrong parts of their body for the IK, which would normally be fine as most weapons are right handed and would use the right side of the body to aim. The bow is using the left, but this character is trying to rotate their right shoulder and arm to point forward for the Aim IK. How to resolve? You’ll need to use offsets or effectors to change the position or have components on the bow itself that alter the full body Ik.