On Minecraft 1.13.2, in the seed 1988960633, there is an igloo that amidst says will spawn, but doesn't spawn at 9464 -21319, and there is a witch hut that spawned, but amidst didn't say it would at 12005 -22684
Can't reproduce; for me, (9464, -21319) is in the ocean, and there is no structure at (12005, -22684).
Are you sure the seed and the Minecraft version are correct?
On Minecraft 1.13.2, in the seed 1988960633, there is an igloo that amidst says will spawn, but doesn't spawn at 9464 -21319, and there is a witch hut that spawned, but amidst didn't say it would at 12005 -22684
I am using amidst v4.3-beta5