The 3 skull Spider boss in the Skittering Cavern is and has been buggy for me for quite some time. When it uses it’s special stomp attack (the one where it jumps into the air) it will glitch up and attack sideways. I’ve even seen it do the attack upside down. When it glitches up with this attack it also doesn’t hit the target (my thrall).
I play SP with no mods.