So it's been awhile since I've hunted here but back recently within the last few months. I am having an issue with the forest vipers in regards to how the hell to knock them down so I can skin them. I seem to remember them being easier to knock down but now I have tried: Binding, Webbing, Arrows, Bolt spells etc. Are they bugged by chance or is there a more specific method needed to knock them down?

I recall there being some unusual behavior for tree vipers in River's Rest some time ago, where even after certain messaging claiming they were knocked down (and they were no longer 'hanging' in the room description), my wife's ranger was unable to skin them.

One tactic that is fairly fool-proof is if you wait for them to attack and drop down on their own. I was using Evil Eye to get fangs for alchemy, and I think it tends to knock them down.

Web bolt was fairly reliable for getting them out of the tree. Not 100% but pretty decent.

Keep some logs and see if you can find any contradictory situations (like where it says they are knocked down and aren't hanging in the room description, but it still says you can't skin them). It would be good to know for sure if this behavior is working as expected or not all the time.