As the title sais
Steps to reproduce:
 - Make some worlds in 1.17 and load all chunks within a a specific render distance (don't move)
 - Update to the newest prerelease and find the border
 - Go along the border and you will sometimes find this

• World Type: "Default"
• No additional generation settings
• Seed: 9184991237633477144
• Coordinates: 118.05 135.51 -293.96
• Render distance used: 16
• World download: https://drive.google.com/file/d/1zcHNn11jWrN8UzUpUWHfEiAXWnoPVl07/view?usp=sharing