We're able to checked the other units and it shows serviceable with NBN connection.
Unfortunately, other than the same information that you have wherein your address is not yet serviceable until June 30, 2020, there's no specific details provided by NBNCo as to why. The serviceability date though is subject to change.
This information is directly from NBN Co.
Hope I was the bearer of a better news, however, we received the update from NBN Co and they've advised that your address is not NBN ready. The planned serviceability date is on June 2020.
There's no other information nor an explanation on why they are not able to provide the service. You might need to contact NBN Co directly on 1 800 881 816 for further discussion.