This happened to me too, I was trying to build a pig farm but failed with this error and had to place it down to the ground.

Seems like dirt blocks or water blocks is not correct ground type for pig spawners to even spawn in

u need a block of grass for it to spawn for some reason, so just have one block of grass and it will spawn it on the one block

it wont spawn due to water being on top

oof

he better have his land claimed lol