Unable to search managers - Act as proxy manager Reward Cloud

The user is an Australia Strategic People Business Partner for a while now but she seems not to be able to proxy in as any of the Line Managers in Reward Cloud.

As she navigate to My workforce > Reward Cloud > Act as Proxy Manager > Click the dropdown button beside her name > Click search

Upon filling in the needed details, ex. name or person number, No display found is the result.

The weird part is that the issue only occurs on PROD and only in one user as other user can search. Also, It does not occur in our lower environment and we checked all the navigation below and all configuration is the same with the PROD, including the roles.