So I started a world in 21w16a with the Caves & Cliffs preview datapack on. After leaving the world for the first time and restarting it right after, massive lag spikes would occur when I cross a chunk border.
Here's a link to a video I made showcasing this bug:
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I just wanted to make a survival world and play a bit checking the new things out along the way and stuff, but this just makes it unplayable...
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ah ok thx for letting me know.

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We're tracking this issue in MC-166005, so this ticket is being resolved and linked as a duplicate.
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Duplicate ofย MC-166005.