When an enemy approaches the crusher, the crusher will predict (I guess) that the enemy has entered its range and start to release the hook. If a blast stuns an enemy at this time, the enemy will walk out range of the crusher in the next frame. ,but at this frame the crusher is still trying to release the hook on that enemy, so the crusher will be stuckit will not be able to release the hook until the enemy moves again.(see the video, the animation shows that the crusher will only try to release). However, upgrade its range or change it target will make crusher release its hook again.