Since you have fruiting Citrus at your place, doesn't sound like a locality issue.
It could be variety related, some Citrus do better in your area than others.
Where is the nearest other Navel Orange to yours ?
That said the Navel originated in Brazil, so you would think it should be ok ?
Also Oranges can behave differently in Nth Qld ( can't we all ). i.e. regreening of fruit on the tree etc.
Could be a rootstock issue, your different trees could be on different rootstocks.
That might influence growth pattern.
Another factor could be constant growth, with no stress period to induce flowering.
A period of drought stress can induce flowering in the tropics, where there is not the same seasonal change as other areas.
As you say could be too happy, possibly vigorous rootstock is pushing it into growth 24/7.
I hope other members can advise on flowering times and fertilisers that might turn it around.