Yeah, this is an annoying aspect of UA's search engine. The trick to fixing it is to find one day on which there is actually nonstop availability in any cabin. Usually, this requires more or less exhaustive searching. In this case, there is good economy availability in the 2nd half of January for AKL-LAX (try Jan. 19 or Feb. 3). Search on that day, and select "nonstop only". Now the calendar will reflect the availability that you want (and you can confirm that there's no J availability on that route in January or February).
As soon as you search a route that doesn't have nonstops available, UA's engine will default to showing connections. Which is annoying, to say the least. In this case, NZ doesn't have any award seats open from Feb. 3 through end of March... which means you can't select a day in March with nonstop Y availability in order to see the calendar for April. So you're left checking days one at a time (including connections)... until you happen to find nonstop available in some class on a day, at which point you can check the whole 2-month calendar around it.
ahhhh.... very good info to have and not something I would have known. Thanks