The jumping spider jump is very fast, shouldn't jumping spiders be hitting most of their targets even without this? (In 0.2 seconds, can an ant walk out of the bite range from the landing point?)Ah no I know what this is and it is not actually a bug. As part of the jump sequence creatures receive a sort of silent stun for 0.2s to allow the creature to reach its target it is jumping to without it moving. It bypasses cannot be stunned checks. This would not normally be a problem but here you have more than 5 things jumping at it a second so it is just stun locked.
If I understand it correctly, jumping spiders apply a short 0.2 second stun when jumping? An alternative to full stun might be mobility only stun? (For 0.2 seconds target cannot move, but can still attack.)You would be surprised. Vs ants yes but vs other fast creatures no. In reality the situation where you have hundreds of jumping spiders attacking is not going to happen so not a problem.