The bug
Found a village that spread into a swamp. Generation of animal pens resulted in lily pads appearing on the ground.
There were also dirt blocks in places that looked to be where the jigsaw puzzle pieces are. They did not generate as grass (like the surrounding blocks).
How to reproduce
Seed: -7437039540087077162
Coordinates: /execute in minecraft:overworld run tp @s 539.65 65.50 -2543.90 -204.86 51.96
Is this still an issue in 19w11b?