I have this 2x2 area that i tried to fill up with dirt but I can't. I can stand in the spot where I cannot place blocks. I can place blocks next to this spot, above this spot, and below this spot but not in this spot. I can have gravel and sand drop into the spot, and I can remove the gravel and sand as usual, but I can't place dirt, wood, stone or any other solid block. I can place both lava and water in the spot and remove the liquid with a bucket, but not by replacing the source block with a solid block except by dropping sand or gravel. If I let sand or gravel down and unload the area, when I come back few minutes after some cows are suffocating under the fallen blocks. If I let the spot empty some cows spawn back and leave the spot but I can't place blocks either.

Animania 1.6.2, Minecraft 1.12.2 on small custom modpack

It sounds more like a glitch randomly happened

@washinoboku is this running on a server?

Never encountered anything like this... please press F3 + B to see hitboxes of entities and tell me if an entity is there.

It was a glitched cow that I solved with MCEdit. Just deleted the block who glitch the cow and the cow itself. I think was a bad mod interactions.
Never try to reproduce it, but I remeber filling an area with the construction wand from extrautilities 2 and suddenly at the same time, a cow walk directly in the space was filled with the wand. The cow dies suffocated and everytime the chunk was loaded, the cow returns and dies.

I'm going to close this as a one-off weird issue that isn't really reproducible.