When falling from any height in survival, your fall damage is randomized. It should be a standard amount, with no randomization.

To reproduce:
1.Equip feather falling 4 boots
2.Make a pillar 25 blocks tall, walk off, and see how much damage you get dealt.
3.Regenerate, your health and repeat as many times as you like. Mark down how much damage you take each time, and you will see it's anywhere from 2 1/2 to 6 hearts.

As you can see this is quite the issue with game balance, and needs a quick fix!