The reason I tested in a FP project was to see if this error is isolated to one project or if it is a bug in ISMCs. Because it works in another project under similar conditions, it is safe to assume that the error in question is either specific to the assets being used or the collision settings within your projectile/ISMC. In this case, because you do not have a box collision/sphere collision component within your projectile blueprint, this could potentially lead to errors similar to what you are experiencing. Try adding a box collision into the projectile and setting the onHit event specifically to this box collision, then set the cube itself to No Collision. Do this and see if you get similar results.