anyone here experience the bug where catching legendary after raid? The ball constantly come off immediately or after one shake. Can't catch any of it for few days already TT

it's not a bug.

Its Obviously the Lowest Catch Rate of Any Pokémon.
You gotta clearify the situation more. Are You not Getting the Spin Bonus?
Are You using Gold/Razz?
Are You getting Great/Excellent?

Hm, I am not surprised if someone fails to catch any legendaries in a span of days. How many attempts already? What surprised me is there is not a single instance of two shakes and then breaking out?

Fwiw, I've gotten the impression over time that connectivity issues can result in lower catch rates. But I can't prove it.

I have had things like low level Karps break out and run at times in those situations. But I'm not experiencing this "bug" on legendaries when I am in a good area so I don't know what to say.

When I've experienced this it's often been shown by more bounces and even a super long pause...then breakout and/or flee. So that does not sound similar at all really.