This is most likely your computer not being able to handle the world generation. Is your computer generally laggy or glitchy?
This bug cannot be verified as there is no proof. I believe you saw what you saw, but since there are no screenshots or videos this bug cannot be verified.
Are you using a texture pack or a mod? If it is a mod, it is likely to be a glitch from there, and therefore not actually a vanilla bug.
Yes, I used optifine. Well thanks, now i know itβs not Mojang's fault!π
Yeah I realised that after I deleted the world. Iβm stupid I know π
Since this is not an official minecraft bug, this bug is invalid. If this bug still happens to you in vanilla minecraft, please do report the bug once again.