There were two issues initially.
When logged in as delegated admin in End User UI, delegated admin cannot view assignments tied to roles visible in UI. After creating assignments, linking them to ldapGroups and associating them to roles these were viewable in IDM Admin UI but not in End User UI
To make them visible: Customer changed the Managed Object > Assignment name (from assignment to Assignment) and that started displaying additional information on the UI.
Creating assignment privilege via CURL works. However doing it through UI returns an error. There seems to be a bug in the UI on property validation.