Crashes when trying to generate new chunks & optimizing worlds problem

I opened the LAN world and enabled cheating. then I switched to spectator mode.

I found a zombie spawner close to x=70.11, y=23.68, z=208.51, i tried to get back to the home close to the spawn. then crashed.

 

after crash, I tried to optimize the world in the "edit" button and join the world. it didn't crash but it shows nothing except the blue sky.