Sorry, I'm not a LH expert at all.
As for getting from AUS-ORD, I see
Mileage Plus award availability --
12/21: I see (3) options AUS-DEN-ORD with DEN-ORD in F. I also see (1) coach award seat AUS-ORD on the noon departure.
12/22: I see (1) option AUS-DEN-ORD with DEN-ORD in F. Also see coach on that route. No award seats AUS-ORD non-stop.
12/23: There's a coach seat on the 9:40am departure AUS-ORD. There's mainline F AUS-DEN-ORD starting with the 9:10 am AUS-DEN. There's also coach on AUS-DEN-ORD starting with the 7am AUS-DEN.
I haven't gone any further.
Perhaps you're running into problems because the ORD departures are via United Express (no F) and many of the DEN departures are UX as well?
Or because they're not checking routings via DEN?
Or because they're not offering you Y connections through ORD?
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View from the Wing: A blog about Free Miles and Free Markets