From the docs:
Getting Scene data on Groups
When getting per-component data, such as PointPosition, the results are correct only when all objects in the group have the same number of components. As a workaround, one possible way to get, for example, all point locations is to plug the Get Data (group) node’s value into the Geometry port of a Generate Sample Set node with Emission Type set to Point and Rate Type set to All Points.
Here’s a screenshot of that workaround:
Compare with: Getting point positions from a group
Suppose you have several objects, and you want to use ICE to add a point at each vertex of each object. If all your objects had the same number of vertices, you could do it by plugging Get Group.PointPositions into Add Point:
But this works only if all the objects have the same number of vertices. Otherwise you won’t get points at all vertices of all objects.
Note that you have to either freeze the transforms on the objects or, as shown above, convert from local coordinates to global coordinates.
To add points on the vertices of any group of objects, you can use Get Closest Points. Just adjust the cutoff distance until you get all the points on the objects.
UPDATE: You can also use Generate Sample Set.
Hat tip: CiaranM