I've been playing the Elemental Prize Fight, and a few times, I've been blocking and the enemy attack went through and hit me anyway. This happened once when a Valentine forward dash attacked, and two more times when a Cerebella and an Eliza tagged in. I definitely was already blocking before the attacks hit. In the case of the Valentine, the attack actually triggered stun on me due to the fight modifier. None of the attacks were unblockable, yet they still went through the block. At first I thought it may have been a fluke, that the block hadn't finished activating when the attack hit, but after the next two times I was sure I was already blocking before the attacks hit.