In Minecraft: Java Edition 1.14.3 (and only in 1.14.3), when running, walking, or turning, a blurry/ pixelated line appears about a third of the way up from the bottom of the screen.

In Minecraft: Java Edition 1.14.3 (and only in 1.14.3), when running, walking, or turning, a blurry/ pixelated line appears about a third of the way up from the bottom of the screen. It will disappear when the player is still.