I don't really know how it works but for some reason I was able to do it plenty of times, here's a recording while I was trying to recreate it, watch it till the end because you can see the actual potential of this there.
https://www.youtube.com/watch?v=eTYeSGawhh0
Edit: Been testing the bug a little more and it turns out it has to do with stamina. When you run out of stamina you aren´t able to climb vines anymore, so you just fall BUT (idk if this is 100% real but it may be) the game still detects that you are climbing the vine, so you are in a state where you are climbing the vines but at the same time you're going down so you are cancelling the fall damage because the game thinks you are just "changing" the vine you're currently climbing.
This means that if you make a huuuuuuuge vine line (it rhymes) from one section to the other, you can cancel pretty much 500 blocks of fall damage.
Final edit: Devs, I feel sorry for you.