Zipline knockdown inconsistent?

[Azula]

I find knocking players off of ziplines inconsistent. I understand that you can only knock down retreating players. However, sometimes a player can get hit and they will not be knocked down - is this a bug, lag, or do I not understand the mechanic properly?

 

[brrr]

The mechanic is that once you've been on a zipline for a period of time (3 seconds I think) you will no longer be knocked off by taking any damage (will still be knocked off by stuns, notably stuff like Grey Talon ult). This resistance to being knocked off is shown by a energy shield that appears around the character, you should be able to see it when you take a zipline.

 

[Azula]

I see, thank you so much!