First off, I play a fair amount of viktor. (weird, I know.) The bugginess of his laser was always painful to deal with. To sum it up, it altered the ability in the following three ways. (In case ya didn't know.)
-When the laser went invisible, which seemed to happen randomly, it was much harder to dodge
-When the laser went invisible, it only provided vision to viktor at its starting location.
-The hitbox was inconsistent and occasionally the laser would pass directly through foes without damaging them.
Following the Kha'Zix patch, the coding for the laser is quite obviously different to fix this problem. These are the aspects of the ability that have changed.
- Firstly, the burn animation on the ground will always appear and follow through the entire animation.
-Secondly, the actual laser effect coming from viktor's third arm will always travel about 2/3 of the way down the burn path and then disappear, as the burn path continues. (The actual death ray halts, but the move does not.)
-Thirdly, the mechanics of the sight granted for viktor's laser were overhauled. Previously, when it worked, wherever a piece of laser was, you acquired approximately a champion's vision from that point. This vision would travel with the laser. With this patch, the laser grants vision for 3-4 seconds for a large area nearby, (I believe it is standard sight from the origin) And then the laser itself will grant very brief and short range vision if it exits this original point. Thus, if you use your laser with the origin outside of the bush, and the bush enters and strikes an opponent, the opponent will quickly leave your vision again, as only the brief vision granting aspect of the laser entered the bush.
Fourthly, the hitbox was shortened slightly at its end. Thus, the range was ever so slightly nerfed.
These changes are overall very good! Viktor's death ray does things consistently now!
I find it strange that these changes went through unannounced, but riot does as riot pleases.
I did quite a bit of googling and couldn't find anybody else that has posted about these changes, and so I figured that I would. Don't hate me for it! :P
Oh, and viktor sucks. You shouldn't play him, because he's underpowered.
TL;DR: Viktor's death ray does not go invisible, and was changed in subtle ways unimportant to people who don't play him.