Something is up with Jhin's ulti, about half the time I use it people tp all over the place, not flashing I know what that looks like, or a blink or dash. They literally just move all over the place like his ulti is losing frames or higher ping. Sometimes the bullets just go right through people too :(
I've been playing a lot of Jhin as well, and I've noticed this as well.
It's hard to describe, but it's as if people just instantly moving 200, 300, 400 units. Maybe it's fog of war nor registering properly, so you think you know where they are, but you actually don't.
Or perhaps you 'save' their location when you press your ult, and while you are zooming out, that location is used, but when you fire the first shot the location updates and they skip all over the place.
