This happens when the ListGen Generator is used for the gen1 Generator of an Attribute within a Domain. If the setLoop Parameter has been set to "True" within the ListGen Generator, users will not be able to alter the Loop Count Value from the Scenario.

The Summary will show N <Domain Name>, and an Edit (Pencil) icon will not be present. 

The Info Icon can be used to view more information.

If the setLoop Parameter is set to "False" for the Attribute gen1 Generator, the Loop Count Value can be modified from the Scenario.