Hill said there were "several missed opportunities" to engage senior consultants which led to a delay in her undergoing surgery to stop the bleeding.
He also criticised the junior doctors for transferring her to ICU or HDU after she collapsed and when a blood transfusion reaction was suspected.
"I share the view that this stemmed from a lack of appreciation of the seriousness of Mrs B's condition and the inadequacy of the blood replacement. The failure to involve more senior staff resulted in poor decision-making across multiple specialities, culminating in a "failure to rescue" Mrs B."
Hill found the level of care given by hospital staff was "sub-optimal" and believes the patient should have been transferred to the ICU after the first emergency call when she was unconscious for 30 seconds.
The woman was eventually rushed to surgery 12 hours later when another emergency call was made. She was taken to ICU but died one week later.
Hill agreed with expert advice that more urgent action should have been taken given that she had lower gastrointestinal bleeding for over 12 hours.
He also criticised poor miscommunication between teams that led to a 48-hour delay in carrying out a colonoscopy, which was "completely avoidable" and would have helped doctors identify the best course of action.
"District health boards have a duty to facilitate continuity of care. This includes ensuring that all staff work together and communicate effectively."
HDC recommended Waitematā DHB apologise to the woman's family and provide the HDC with an update on its progress on recommendations from its own review of this case after it carried out a serious adverse event report.
HDC also recommended it carry out an audit of documentation to ensure that treatment plans and discussions with other specialities are adequately documented.
In a statement, Bryant said Waitematā DHB had already made "major changes" to the way its medical wards operate to "significantly reduce the likelihood of a similar incident happening again".
Changes include implementing an electronic programme that helps identify patients whose condition is deteriorating, assigning dedicated medicine teams to each ward and opening a dedicated gastroenterology ward by the end of the year.