Sometimes, I randomly experience unintended and weird fall damage. So I tried very hard to reproduce the glitch.

This subtle range of block causes fall damage glitch. I even don't know if the character actually steped on the block. Sometimes, you won't get any fall damage as much as you expected.

try the world with trapdoor first please. If you open the map, just keep sprinting follwing the iron blocks aligning.

If the trapdoor world doesn't work, try one without trapdoor.

I recorded these on Win10 x64,

using NVIDIA GeForce GTX 1060 3GB,

Intel(R) Core(TM)  i5-6500 CPU 3.20GHz,

16.0GB RAM.

+ android 8.0.0 is also affected

+ Maybe this ticket is related or not! In the slime world, which is with a slime block on the ground behind the iron block, most of a time you won't get fall damage if you just walk following the iron blocks. Not 100% for sure

https://bugs.mojang.com/browse/MCPE-151015