The product uses multiple resources that can have the same identifier, in a context in which unique identifiers are required.
If the product assumes that each resource has a unique identifier, the product could operate on the wrong resource if attackers can cause multiple resources to be associated with the same identifier.
Where possible, use unique identifiers. If non-unique identifiers are detected, then do not operate any resource with a non-unique identifier and report the error appropriately.
If unique identifiers are assumed when protecting sensitive resources, then duplicate identifiers might allow attackers to bypass the protection.