Board Thread:Bug Reports/@comment-73.20.240.132-20170429200929/@comment-25565811-20170429210938

You can check what region files it is in and delete those from your saves folder. They are stored in saves/yourworld/MiddleEarth/region and called r.x.z.mca. You calculate the region indices by deviding your world x/z coords by 512.

Make a backup copy before you delete any files to keep your world safe. After deleting the region files, visit the region again, the chunks will be regenerated.