So what gives?
As per comments and responses above pax were supposed to clear instantly, since there's sufficient pn space for both passengers on the outbound, GPU was applied however and no clearance, just added to waitlist.

Here's current fare inventory.
Los Angeles, CA, US (LAX) to Melbourne, VIC, AU (MEL - Tullamarine)
UA 98 | Boeing 787-9 Dreamliner

Depart LAX: Tue, Jan 19
Arrive MEL: Thu, Jan 21
Red-eye flight
Available fare classes:J9JN9C9D9Z9ZN9P9PN3R0RN0IN0I0Y9YN9B9M9E9U9 H9HN9Q9V9W6S4T0L0K0G0N0XN0X0

Any insight or advice would be appreciated. Thanks