Rendered chunks disappear and never return

Days before this happened the chunks of the world were fine and rendered in perfectly fine but now there are chunks missing and many attempts of making them appear again have failed, ex:closing game and reopening,copying world, and leaving world and loading back did not work.I don’t know what’s happening but this has only happened to 1 world I have which is (infinite flat) and i don’t what to do now that this has happened but please help...