Bamboo in bamboo jungles and kelp in oceans noticeably generate in a chunk-based grid, unlike other features. This is especially visible at biome borders.

Reproducing the issue

Kelp

Create a "Single Biome" world with the biome minecraft:ocean and the seed 1234567890. Run the command /tp @s -85 78 -334 20 65. Enable the display of chunk borders and observe the pattern of kelp generation. The attached image "kelp.png" shows this pattern.

Bamboo

Create a "Single Biome" world with the biome minecraft:bamboo_jungle and the seed 123456789. Run the command /tp @s 61 91 -17 -105 60. Enable the display of chunk borders and observe the pattern of bamboo generation. The attached image "bamboo.png" shows this pattern.

Note that this generation is not limited to Single Biome worlds—they only make it more apparent.