I just had an 'the ground is shaking and strange noises are coming from your feet' event, and the coordinates it had pointed at a pool of water. I think it ended up being negated by it... Your code should probably make sure that the target area has land for the thing to spawn on?

Yeah it should. Will make some changes

Enemies still sometimes spawn on islands.
Can you try placing a pathfinding request to the center of the map that ignores player creations, and only spawn if that location succeeds?