Please see explainer video: https://youtu.be/8EYrVxP6sA4
Various chunks around the world are "corrupted", "broken", "slow", "laggy" where redstone does not fire properly and water does not flow properly.
Redstone becomes extremely slow, with a delay of several seconds before it activates and water flows extremely slowly.
This can happen in 1 chunk next to another chunk which is completely fine.
Removing farms, redstone, hoppers and pistons in the area does not improve anything.
Render distance is on minimum, mob spawning is off, no command blocks active and all entities have been wiped from the world.
Toggling the difficulty to peaceful and using commands to kill all entities in the loaded areas does not fix the problem.
The problem is not due to lag as the chunks next to the corrupt chunks work as expected.
This happens on Minecraft Bedrock single player worlds and Minecraft Bedrock Realms.
This is currently affecting version 1.12.0 across all devices.