Ivara Sleep arrows only sorta effective vs Plains creatures.

[Oreades]

Ran into an issue when I was popping a riven and it isn't the first time this has happened with the "Kill X animals on with a fishing spear" challenge. 

In short while cloaked you sneak up to them, shoot them with a sleep arrow, switch to your spear and start killing. 

The problem is that the sleep arrow doesn't seem to pause the rodents "burrow timer" so they can be functionally asleep and just nope out anyhow. Which is especially noticeable the closer you get to that timer running out. For example if you chase them down and sleep arrow them after they've run for a bit they will "pause" and before you can switch to your Fishing Spear and well before your sleep arrow will have run out they will burrow away.  

The Conderoks also have a similar issue where they are and aren't effected by the arrows at all. In that you use the arrow and they will appear to pause they will get the sorta aura glow indicating they are effected by the ability and then the second you use your fishing spear on any of them the other two will instantly fly away as if they are unaffected by the ability. 

It's just a bit inconsistent with the sleep arrow mechanics in the rest of the game. 

[Wyrvox]

I can confirm this bug. The sleep arrow did work correctly on the plains animals previously the last time I had this riven challenge.