Sometimes when mobs fall from certain heights don't always seem to avoid damage when they fall on blocks that negate fall damage. In this case, these blocks are:
Cobwebs
Berry bushes
Powder snow(fixed in 1.18 pre-release 2)Ladders, vines & twisting vines (On players case see: MC-185695)
This report only covers mobs, not players. There are some cases in which players don't get fall damage on some of these blocks, but the fall damage sound still plays (MC-205097 / MC-230981).
Some of the heights where this seems to apply are: 20, 23, 25, 28, 30, 32, ... , above the block (i.e. 25 blocks above the block below a cobweb). Water blocks are not affected.
How to reproduce
Make a 3x3 of cobwebs, bushes, or any of these blocks.
Walk to the center of these blocks.
/summon husk ~ ~25 ~
❌ The mob either dies or gets fall damage.
Trying to use powder snow to reset fall damage in my mob farm and run into this as well, but it seems way worse - pretty much any height high enough kills the mobs, except for exactly 26 blocks above for some reason.