Through testing with ERPNext using different user role, I think there might be a problem with ‘Linked with’ button. When you click that, it scans all Document that is linked to the current Document.
It is perfectly fine if you are Administrator. However, if you have only certain permission, there is a high chance that you will be stopped before retrieving anything by a Not Permitted error. This is understandable because it scans every DocType available.
But as a Sales Manager/Sales User. I want to know which Sales Order linked to which Delivery Note. And this prevent that to be accomplished.