Custom Buyer Responsibility Not Available when attempting to Secure Content Zone by Responsibilities

I am attempting to secure a content zone by a Responsibility. The Responsibility is a custom Purchasing Buyer responsibility. I have ensured that the MO: Operating Unit profile value is correct, and the MO:: Security Profile. When I search for the responsibility, it is not available. The vanilla Purchasing Buyer responsibility is available, as is our custom Internet Procurement responsibility.

Any help would be appreciated.