In Collaboration Hub (preview or published mode), even though all attribute visualisation options are selected, the 'task' attribute panel not showing paperclip icon or linked document which is linked to a dictionary item which is linked to a BPMN 2.0 element custom attribute
The behaviour you are experincing (i.e the paperclip icon and the attached document not appearing in the attribute panel) is normal system behaviour.
The attribute panel in Collaboration Hub shows elements like files that are linked directly to the selected item. In your situation the document is linked to a dictionary item that is then linked to the element via its attribute 'SAP Transaction Codes'. This is why you have to go a level deeper in the Collaboration Hub and click on the Dictionary link to see the linked document/file.
KBA , BPI-SIG-PM-DIC , Dictionary for SAP Signavio Process Manager , Known Error