If the velocity is quite high, the period of time when the cube is within the Collision Box may actually fall between ticks. I suggest finding the Use CCD checkbox (both in the wall and in the launched cubes) and tick it. Thus the launched cube will (well, should) always stop upon hitting the wall and actually be within the Collision Box.
Unfortunately, the Continuous Collision Detection (CCD) only works with blocking, not overlapping, so if there’s something to block the projectile, like in your case, that’s fine; but if the Collision Box is on its own, that won’t probably work.