This is a seemingly random glitch that happens while sprint jumping to different elevations (or even when elevation does not change).
What was expected:
No fall damage when falling 1 or 2 blocks total.
Fall damage occurred at seemingly random instances when landing after falling 1 or 2 blocks (not enough to induce damage).
Steps to reproduce:
1. Go into a world and travel in a landscape with plenty of small elevation changes (sprint jump with small hills).
2. Keep doing this. Eventually (10 minutes maybe) you may receive fall damage. It seems completely random, but it only seems to happen while jumping and sprinting (which most people do because it is generally the fastest way to travel, at least faster than running alone).
I'm sorry if this is a duplicate, but when I searched my issue I only saw glitches that apply to multiplayer or ladders or stairs. This happens anywhere and on singleplayer. My world is not modded and cheats have never been enabled (this is my achievement world).
I managed to upload two videos as evidence. In one I take damage from two 2 block falls in a row. In the other I take damage from a 1 block fall right after jumping.