It's a bug I've noticed on other versions like 1.16 to current 1.17.1 version. When I place farmland most of it will be fine and nothing to worry about, except when I begin placing more then a bunch of between 4x4 to about 6x6 patches stop working. You can hoe the grass/dirt and it will accept water sources but you cannot place any crop onto them. I've reloaded Minecraft, tried breaking the blocks and redoing it but nothing is working. Even tried moving the farm incase it was something to do with the chuncks it was in but that still didn't work after placing more.

Please take a look at this cause it is very annoying especially with trying to make big farms. 

Cheers