Looking to confirm what an agent told me today.

I booked SYD-LAS, 17 Oct, UA842/2288 in G. SYD-LAX shows PZ4, so I went in an applied a MUA (30k/$600). The MUA screen showed "Available" for SYD-LAX, and "Waitlist" for LAX-LAS. After finalizing the purchase, both my flights show "waitlisted" in my reservation. I was under the impression that applying a MUA with PZ>0 would automatically upgrade the available segment. Agent said this:

Agent: Thanks for verifying. I see that you used miles for the upgrade. Just to give you a heads up,MileagePlus Upgrade Awards is a waitlisted upgrade. And for reference, the timing of upgrade confirmations is based on availability and status level: 1K: 4 days before departure Platinum: 3 days before departure Gold: 2days before departure Silver: Day of departure

Agent: I'm sorry but it is a waitlisted even though there's PZ available. You will be confirmed form the upgrade 48 hours before your flight. As much as I'd love to help you but it is a system generated process and we don't have a way to override it. But you are currently 1st on the list for both segments.

Just looking to verify - previously used PP for immediate upgrades w/ PZ available, first time using MUA (Gold now, previous 1K).

Appreciate any advice.