Describe the bug

Preexisting chunks near my base are suddenly elevating 10 to 20 blocks.
To Reproduce
Steps to reproduce the behavior:
N/A
Expected behavior

Not have preexisting chunks suddenly elevate.
Screenshots

https://drive.google.com/drive/folders/18x-F6IUPh_fAmVNK3rYIVAuxGWOLFoX9?usp=sharing
Info (please complete the following information):

• Modpack Version: 2.77.5
• Server or Singleplayer: Singleplayer
• Version the world was created on: 1.12.2

Additional context

Stale

The heck? Could you send latest.log in the logs folder?

Need logs, this looks like world corruption