Cannot find user to set up vacation rules

Summary:

Hello we want to set up a vacation rule for one of our users, but they don't come up when searching the Identity Browser. What do we need to do to be able to search and set up this person's vacation rule?

Content (required):

• I have the correct access and am able to search for other users.
• I have checked their person management and User account profile and was unable to identify an issues that might be causing this.
• I am able to search the user in non-prod but not prod.
• I tried searching by on First name, Last name, email, ID and various combinations of the listed options.