Nerfality [NERF]
Thief Withdrawl vs immobilize
Judging by the video you provided, the spider’s immobilizing ability seems to “pulse” (i.e. it hits two times with a short pause between each individual hit) and ignore evasion skills. You could test this by letting yourself get hit by this attack again and watching the immobilize’s duration: if it is reapplied before it first runs out, the above theory is likely to be true and Withdraw working as intended.