Had a similar experience in Sydney this month, was informed the LAX flight would be 2 hrs late so took it easy to the airport - to find the United check-in was just closing and the staff walking away.

The problem is, UA fired its Australian check-in staff last month and now outsources the check-in etc to another company. Who are only paid for the planned check-in hours, regardless of how late the actual flights may be.

So if you hear that your flight from Sydney will be some hours late, too bad, you still have to get to the airport an hour ahead of the original departure-time or there will be no one to check you in.