Arena- gas doesn’t get AB from Vader basic

Noticed this happening during the LV vs JMK Cat fights. When it gets to the end, for some reason Vader’s basic should land ability block 100% against Jedi. But it never does. It lands the first few times I basic gas during the MM. but for some reason when I get to this spot - he never gets ability block. https://youtu.be/Qih5WIpRnHM