[1.8.9] Spawn falling blocks

Alright I feel totally retarded to ask this.

I am triing to spawn blocks of falling sand, but for some reason they are appear for a second and disappear right away.

this is how I spawn the block

int x = world.rand.nextInt(sizeX);
int z = world.rand.nextInt(sizeZ);
EntityFallingBlock block = new EntityFallingBlock(world, anchor.getX()+x, anchor.getY()+18, anchor.getZ()+5, Blocks.sand.getDefaultState());
world.spawnEntityInWorld(block);

(It gets called on server side every 5 ticks if some conditions are true)