Minecraft wiki entry for Chunk, associated text: In Bedrock Edition, when toggling fancy graphics, the world renders again, loading only the chunk the player is in for a split second, briefly showing the chunk boundaries. When the player changes the render distance rapidly, chunk barriers appear as a blue line. Also, if in mid-air and bridging with full blocks, when a chunk border is intersected the next block placed will fade into view, showing the chunk border. This is sometimes unreliable, but useful as it only happens on chunk borders. This does not happen underground or when the block placed is close to more than one block.