Let's imagine your name is Simon and you've just added Moe as a new administrator. The first time Moe signs in they will only see the positions that they have been granted hiring manager access to.
So if you create a new role Moe will not automatically have access to it. You'll need to add them. Likewise, when Moe creates a position they will need to add you as a hiring manager if they wish to allow your account to view their hires. We set it up like this to ensure that a) we allow for multiple teams within an organization to assess their candidates separately and b) people who were recently hired by Plum and given an HR manager role and therefore a Plum account do not see the applicants that they competed with for their role.
Contact your success manager if you have more questions.