I have a 1.14.4 survival world, and when I reloaded the world to play, some random chunks from a mountain biome were swapped with chunks from a nearby plains biome, resulting in large stone pillars in the world.
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Thank you for your report!
We're actually already tracking this issue in MC-150202, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.