That could be it...i thought i was using the same level of equipment as i last fought them with but even if i am its possible the shield stats were changed with the update. They're just the first mob i've run in to where the stagger time has been noticeably different so i jumped to the assumption it was a mob thing but it would make more sense if it was equipment. I'll have to craft a higher level shield and see if it staggers them longer.