In my other report they closed the issue and said it was a dupe of world chunks having holes well the not buffering situation is different. This is causing that issue but in itself different. The world is having difficulty loading the chunks in the first place upon loading a world and if you get ahead of that loading system for a second it takes a full minuet before it's fully loaded. This needs to be fixed

Not loading even when on top the wholes some time was mentioned here but, they closed the entire issue instead of part of the issue.

The main difference is once you load a world it has difficulty loading them unlike 1.8.1 as if it can't this is a separate issue
https://bugs.mojang.com/browse/MC-121707