When a record is viewed in the platform view, if a related list has Hierarchical lists checked, we can see the record hierarchy.
The same hierarchy cannot be seen when the record is viewed in Agent Workspace.
Agent Workspace just shows the parent record (or the record which is at the top in the hierarchy)
This is an expected OOB behavior.
Validated on Madrid Patch 4a.
As a workaround, you can create a custom UI action for Agent Workspace which will show the hierarchy.
OOB we already have a similar UI Action available for Account Hierarchy.
You can refer to the:
UI Action - Account Hierarchy (/sys_ui_action.do?sys_id=5c1e9048b380130082186e5f26a8dce2)
Script Include - AccountHierarchyUtils (/sys_script_include.do?sys_id=3e13d750b3f3030082186e5f26a8dc17)
Documentation - Enable UI actions for Agent Workspace