Almost 90 per cent of all complaints received by the federal anti-corruption body's watchdog concerned the commission's decision not to investigate referrals over the illegal robodebt scheme.
The annual report for the Inspector of the National Anti-Corruption Commission, which provides oversight of the federal body, revealed it received more than 1300 complaints in its first year of operation.
Of those complaints, 1164 concerned the decision by the anti-corruption body not to investigate six referrals from the robodebt royal commission.
In October, inspector Gail Furness announced commissioner Paul Brereton engaged in misconduct after failing to recuse himself from the investigation after a conflict of interest.
Ms Furness recommended a review of the decision should be conducted by an appropriate person, after Mr Brereton declared he had a close association with one of the people referred to the commission.
The annual report said many of the complaints received about the robodebt decision said the commission's decision "disregarded, disrespected or misunderstood the royal commissioner's referral".
"The inspector considered that one or more of these complaints could amount to agency maladministration or officer misconduct," the report said.
The report also detailed a complaint it received in January, after the commission rejected a referral to investigate corruption.
"The NACC told the complainant that they were not able to identify a corruption issue. On the inspector's assessment, there were two identified corruption issues," the report said.
"After the inspector's requests for information, the commissioner conducted a more detailed assessment than had been done initially. The Commissioner agreed, albeit on a slightly different basis, that there were two identified corruption issues in the referral."
