Wolf Spiders randomly cannot be hit by ANY skill. For the easiest way to reproduce the bug, try casting an ultimate. It will randomly fail to hit Wolf Spiders for no reason at all. It won't MISS, it simply doesn't hit, even if there is one RIGHT IN YOUR FACE and you're nowhere near hitting the limit of how many mobs you can hit with a skill. This leaves you vulnerable and makes you take unnecessary and unfair damage. No other mob to my knowledge is bugged out to be unattackable at random (except for Extra B but nobody trains at Showa anyway, unlike Wolf Spiders). I tried Dray's suggestion of CC'ing but it didn't work. In fact, CC'ing then going back to my original channel crashed my game without any error message.
This used to happen in Ghost ship sometimes too. The only solution I know of is having a gm refresh the map. It's a weird occurrence for sure.