From the ASADA site.
Rule violation management process
"We are unable to discuss specific details of its intelligence and investigations programme. We are bound by the ASADA Act and ASADA Regulations, the Code, the WADA International Standard for the Protection of Privacy and Personal Information and the Privacy Act. All of these documents contain provisions that regulate when and what we can say about individual matters."
It appears to me, that it has been decided that "Procedural Fairness" is more important than "Natural Justice". That was certainly argued in the Essendon Football Club saga. I agree there is a good argument for that. I certainly do not want a error in procedure creating a loophole that allows drug cheats to beat the system. Providing a fake sample or failing to provide a sample is certainly not a loophole that you would want to make available to drug cheats.
Sun Yang failed to provide a sample in September 2018. It was February 2020 before the World Anti Doping Authority appeal overturned the (incorrect) FINA decision and an 8 year ban was implemented.
Getting the right answer is more important than providing a quick answer. Willi Rioli is no more entitled to get a rapid answer to his outcome than Sun Yang was.