Loading any map, navigate to a stream or ocean with seagrass generating near the shoreline. On some blocks near the shore under water that should be dirt blocks with seagrass generating on them, grass blocks are generating under the seagrass (and water) instead.

This affects not only new worlds/chunks, but also existing chunks from worlds created in previous versions.

Additionally, the game slows down extremely when around water with grass blocks generating, to the point where mobs will take a step every second then stand still, with no fluidity of movement. It is not an FPS issue, but essentially feels like the system is trying to simulate more than it can possibly handle, or that it's trying to action everything in the entire chunk in the exact same tick.

Not sure if this affects more than the Nintendo Switch version, but it affects new installs as well as updated prior installs.