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How to Reproduce

1. /give yourself a command block
2. Place the command block down and make it a repeating command block with either a redstone source block or have it set to 'always active'
3. Set a game difficulty within the command block

What Happened

• Everything that is considered an 'entity' has EXTREME lag.
• Hitting an entity will make the entity get pushed back as normal but it
  will take a long time as the entity floats up and back down with lots of
  choppiness
• Throwing down items will take forever as when you throw an item
  down. It doesn't go to the ground right away. It will sort of bounce and
  judder up and down until finally it hits the ground
• Picking up items from the ground will take about 3 - 5 seconds
• And much more...

What I Expected to Happen

I expected everything mentioned above to not happen...

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Bug Prevention Tip

To all switch players who encounter this on a map or something try to locate where the maps command blocks are and disable the repeating command block that sets a difficulty. But you might not be able to or you won't be able to go into creative because the map won't allow you too which is why this is a CRITICAL ISSUE