[0.3c] Some red-glow boss attacks are blockable (and viceversa)

I'm playing a warrior with a shield and i'm constantly using the active block skill.

In my playthrough, i discovered that some red glow boss attacks are actually blockable (miller attacks, candlemass attacks, even some of Count geonor attacks), while others aren't blockable at all: Hyena boss slam attack isn't blockable, and that attack isn't red-glowed.

This is also true for white enemies: the mawdun quarry goliath's wheel attack isn't blockable.

This stills happening. Also noticed in the sunken city fatty guys and their slam attacks. I was trying to play around positioning but there wasn't the case.