To put it simply, damage prevention for blocks (including: scaffolding, lava, vines, ladders, twisted vines, weeping vines and cobwebs) is unpredictable and rarely works. I believe this is something to do with the game only checking for these blocks every game tick, which causes problems when falling over at 20 blocks/second.
Steps to reproduce: Fall repeatedly from multiple different heights onto any of the aforementioned blocks
Observed results: Player fall damage is not correctly reduced/cancelled
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We're tracking this issue in MCPE-153117, so this ticket is being resolved and linked as a duplicate.
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