Just because a fare is filed doesn't mean it is bookable. If you can't locate it through an OTA or google.com/flight or ua.com it's not bookable.

Not uncommon - airlines do this often. They'll put the fare out there so they don't have to go through the process of re-filing it but they won't put any seats in the fare bucket required (in this case G).

A quick search shows UA booking into W which is a mid-tier fare bucket (G is a highly discounted fare bucket) - it would suggest at this point they still think they can get a premium for the flight and haven't opened up the cheaper fare buckets.