Minecraft wiki entry for Historical_effects, associated text: Every power of 2 that the player goes, the hitbox of the block that the player is facing becomes more and more distorted.
The hitbox becomes increasingly more corrupted and distorted until it disappears entirely at X/Z ±2,147,483,648.
X/Z ±2,048: Hitbox begins to flicker slightly around blocks.
X/Z ±131,072: The shape of the hitbox begins to deform.