Flat map doesn't automatically generate chunks any more

After the recent update, I have found that my map (flat, creative mode) doesn't generate chunks any more. Farther places I explored would just be vacant as shown by the attachment. I swear that I didn't manually remove it. I really hope this bug can be resolved soon so that I can keep my building my map. It is really inconvenient to have such a map that would not provide infinite automatic generated chunks. Thank you! Let me know if you need more information!y