How far off is the height position? If it only needs to be moved a very small amount to be visible, my guess is the point cloud is in the right position, it’s just exactly on top of Cesium World Terrain. There’s a few ways to resolve it if that’s the case, see the discussion here: How to get more zoom level on 3D Tiles with Terrain.
Otherwise, it might be that the vertical datum in the LAS file is incorrect or not supported. Note that heights in CesiumJS are relative to the ellipsoid.