How to reproduce bug:

1. Create a creative warm ocean buffet world.
2. Place a block using a command so that you can start building in the first block layer of the ocean.
3. Using any block, start building from that point.

This also happens more noticeably when I use the following command in a command block: execute at @p if block ~ ~-1 ~ minecraft:water if block ~ ~ ~ minecraft:air run setblock ~ ~-1 ~ minecraft:white_concrete