Comment 2 for bug 1788722

https://github.com/openstack/charm-ceph-osd/blob/master/lib/ceph/utils.py#L582

 child_ids = json_tree['nodes'][0]['children']

This is the root cause.

the ['nodes'][0] denotes look at the children of the first entry in the osd map which is typically the root OSD pool that has all hosts. however, with multiple pools, we need to find all node members that have children to list hosts in all pools.