Jax's entire kit needs massive fixing
Almost all his skills are bugged in one way or another.
When Jax's leap strike is interrupted mid leap, sometimes the damage will go through on an enemy champion and sometimes it won't. Whatever outcome is intended this needs to be consistent.
Jax's counterstrike has no consistency in it whatsoever. The skills it can dodge and can't dodge aren't made clear in game or by coding. He can dodge the entirety of a Gangplank/Ezreal Q, but he only dodges the AD portion of a nasus/garen Q? He dodges the entirety of Irelia's AAs during hiten style but he doesn't dodge Kayle/Kogmaw on hit buffs? Can this be fixed to be made consistent please?
Also, Jax's ultimate proc has a bug that's been in the game for awhile now and it's never been fixed. Sometimes after pausing his autoattacks, the third hit proc will only take two autoattacks instead of three; i have no idea why this happens or why it's even intended, but here's a video of it happening from a year ago (It's been in the game since 2012 though). Notice how after his ultimate procs around 13 seconds, it only takes 2 hits to charge it again.
https://www.youtube.com/watch?v=5fnLsi6kNmY
His kit is ancient and needs its bugs fixed ASAP. You fixed his laggy as all hell autoattack animation a few patches ago but he has so much more wrong with him that needs work.