Role delegations - not displaying any user LOV

Summary:
There is a requirement where an employee is on vacation leave and want to delegate his roles to another employee for 1 month. Here I tried to Role delegation and worked on Test Instance, but it is not working in the Production instance even after having all Access and role is also enabled for delegation, Delegated To field is not showing any users to select for role delegation.

Content (please ensure you mask any confidential information):

Delegated To Field is not displaying any users to select to delegate role in PROD instance but working fine in TEST Instance.
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