Here is a Short video that shows the mob animation cues are not playing consistently. First group of three the one in the middle does not give the cue and I get knocked on my rear. The second group of three, the one on the left plays properly and I'm able to block it. I'm not sure what you call this cue but you can see what I'm talking about if you compare the two mobs doing a WB. I would call it the charging or channeling animation.
https://youtu.be/AVvDnj5NspM
Proud member of the Psijic Order - The first wave - The 0.016%