I've only played J4 a very small amount of times, but in the few games that I've played him I've had the same problem. Both against Ahri, if she hits a charm while J4 is in midair while casting cataclysm, his ult will go on cooldown, create no terrain, and do no damage. I'm not sure if other cc can do the same to "break" his ult, but this one is quite annoying.
It should have nothing happen, from my experience if you get in a form of cc that moves you to or away (trist or ahri) they stop your ult but doesn't put it on cool-down. Sometimes it would put the terrain down but not go on cool down lol, pretty glitchy, hope they fix this tho, ruined some ranked games for me
I've had it happen multiple times with multiple different champions and it won't go on cooldown; but for whatever reason once his animation starts, it goes on CD and if you happen to die in the midst of it, oh well I guess.
