I noticed a bug in version 1.14.2 pre2 which is still noticeable in version 1.14.1. I experienced extreme lag when placing a block in empty part of the chunk (even if the chunk is totally empty).

How to reproduce:

1. Create a new world with void preset (super flat & creative).
2. Press Alt+F3 and F3+G to show chunk borders.
3. On the generated platform go the to bottom-left (lowest X and Y in the chunk) and run the following commands:
   /fill ~ 80 ~ ~31 80 ~31 minecraft:quartz_block
   /fill ~ 80 ~ ~15 80 ~15 minecraft:air
4. Fly up the level 80 and put it a block (like on the image „2.png”).
   You can noticed the lag, on the FPS counter. This will happen just ONLY for crossing in a new chunk and if the last used chunk part is lower with 2 segment (shown in image “3.png” and “4.png”).