Blocks disappearing after world save

After I place the blocks and then I leave the world (it saves after I leave, of course). Then I go back into the world and the blocks that I placed are just gone. I’m not sure if this is normal since I’m placing these blocks where there’s water underneath.

 

Due to the file being too large, here is the link: https://1drv.ms/v/s!AvBjuMR00empalS6AlzJYYVgyx8?e=ngbHVx