I don’t know what it was like before, but LAS-LAX at 4:35 is X0 now. And J0 as well.

that said, UAs engine will do a mixed cabin for awards. I’m not sure if AC will, at least on partner metal. Id guess that’s a reason it’s not showing up. I’d also assume UA would have to have [additional] open space on the SYD flight, which is J3, I0. Not to mention, would need to be married segment availability. So there’s 3 potential reasons - any one of these is why it might not show up.

seems things are being made more complicated then they need to be. OP can either show up for original flights and hope all goes as planned (who knows, it might!) and like many of us, deal with IRROPS if and when they happen, try to call and see if UA would do an SDC to a lower fare class on LAS-LAX on earlier flight, or show up and try to standby.

Again, booking the flights with a connection time you are comfortable with is probably ideal in the first place. I get you book based on what is available for the points one has. But we often need to either deal with the uncomfortably tight connection and deal with IRROPS as it comes, or deal with a long connection and make the best of it (work at the club…plan a mini-vacation in the city, etc.).