Most common cause of the symptom
You are an External User on the Project. External Users on a Project are only able to see Open Lists.
Other cause of the symptom
The list is set to Private and only the User who created the List is able to view it.
Insite Teams Projects can have three types of users; Project Admins, Internal Users, and External Users. Project Admins & Internal Users are Users who are also a part of the Plan associated with the Project. External Users are Users who have been added to a Project but are not a part of the associated Plan's Organisation List.
External Users have fewer permissions on a Project as these Users are likely not a part of the organisation who owns the Plan. For example, these may be sub-contractors to the organisation or their client or consultants. These External Users can be invited to a Project so that they can view and add to certain Lists (Open Lists) but are blocked from viewing other Lists (Internal Lists). Please see: Change the privacy settings of a List which gives further details on the permissions of the different users.
Internal Users also have the ability to create Lists that are just viewable to themselves (Private Lists). The Lists cannot be seen by any other Project Users including Project Admins and other Internal Project Users.
1. If you are an External User and you are supposed to see a List then contact the User who created the List and ask them to change the privacy setting of the List to Open.
2. If the List is set to Private then contact the User who created the List and ask them to change the privacy setting of the List to either Open or Internal, depending upon your role on the Project.