The filled-up chunk error from Version 1.8 or 1.9 is probably back.

Somewhere in the generated world, you can clearly see where the chunks were filled up.

Expected: Finding natural caves going on through the different variations of stone, dirt, gravel etc.

Instead: Some of the caves are somehow "cut off" at the chunk borders (while others are not) and those chunks are often filled up, usually with regular stone.

Reproduce: 

1. Create a new world, use Demo seed "North Carolina" or "-343522682" and choose creative mode.
2. Change to spectator mode ( [F3 [n] ] )

3. /tp @s -48.42 18.94 0.10 -463.95 55.80

1.  Show chunk borders ( [F3 [g] ] )
2. Looking north or east, you can clearly see the nearby generated cave being "cut off" (or filled up) at the chunk borders.
3. Continue looking east, you can spot some other caves and even base level lava lakes cut off at the same chunk borders (z=0/-1)

Errors like these can be found throughout the world – probably any world – and are quite irritating....