This can happen when a role is marked Inactive before a user is removed from the role. The role disappears from Role Membership but the user is not actually removed from the role. If you activate the role again under Manage Roles it should reappear on the user's profile.
To activate the Role...
1. In Core > Users/Access > Manage roles
2. Locate the Role and click to open it.
3. Under Properties > Click Edit
4. Mark the Checkbox next to Active
Steps to Duplicate1. In Core > Users/Access > Edit User Profile Data
2. Search for the User
3. Note that Cloned Role does not appear under Other.
4. Switch to Manage Roles
5. Select Role > Members
6. Note that user is still a member