T&CS have been updated to reflect the change -
What are eligible items?
You receive free delivery within Australia if your order includes at least $39 of eligible items. Any item that is sold and fulfilled by Amazon AU, or sold by a third-party seller and fulfilled by Amazon AU, and has 'FREE Delivery' eligibility messaging on the product detail page is eligible and contributes to your free delivery order minimum of at least $39.
Cancelling items, combining orders, or changing your delivery address, speed, or preference might affect your order's free delivery eligibility.
If your order doesn't qualify for free delivery:
• The order may contain ineligible items such as items sold and fulfilled by third-party sellers, bulky goods or special products.
• An eligible item may have been cancelled resulting in the order total falling below $39.