The North Wales Health Alliance (NWHA) said a Betsi Cadwaladr University Health Board report highlighted serious issues around patient safety.
The pressure group said it meant, in some cases, the board risked breaking the law.
The board said it was already working on measures to reduce risks.
The findings of the annual safeguarding report were presented to officials at the health board last week.
It outlined 13 'red' areas of risk, including:
The concerns by the NWHA come as the board meets on Thursday to get the latest update on two inquiries into events at Glan Clwyd Hospital's Tawel Fan ward, which closed in 2013.
"A year and a half after going into special measures and receiving additional support, we have to ask whether Betsi Cadwaladr is learning lessons and making improvements?" stated Marc Jones, from the NWHA.
"These are not trivial issues but are serious risks. The scandal surrounding Tawel Fan should have been a wake-up call regarding the need to take at-risk patients' safety and well-being seriously.
"We do not want to see a repeat of that."
The health board's own analysis of its safeguarding weaknesses highlighted "unclear" policies, little evidence of sharing good practice, and relatively low uptake on safeguarding training.
In an independent investigation in May 2015, relatives said patients on the Tawel Fan ward were treated like animals in a zoo.
It led to the health board being put into special measures by the Welsh Government, and its former chief executive stepped down.
Betsi Cadwaladr board members will be told later that the current inquires into what happened are expected to continue until the summer.
Responding to the NWHA criticism, Dr Evan Moore, the board's executive medical director, said "positive action" was already under way and have continued since the safeguarding assessment was made in autumn 2016.
"The committee recognised that these had lowered our exposure to the risks in many areas and as a result agreed that the associated risk scores would be reduced.
"The board will consider a detailed report on this in public at its full meeting in March."

However, the director-general of the Australian Security Intelligence Organisation (Asio), Duncan Lewis, said there could be no guarantee of safety from extremist violence in the future.
Mr Lewis was speaking after the Paris attacks in which 129 people died.
The Islamic State (IS) militant group has said it was behind the attacks and warned of further violence.
Mr Lewis told Australian broadcaster ABC that while there was no evidence of a specific threat against Australia similar to the attacks in Paris, the number of potential threats had increased in recent years.
"We have had three attacks involving fatalities and six thwarted attacks in the past 12 months," he said.
"To put that in some sort of historic perspective, that represents just over a third of the attacks or planned attacks that we've had in this country over the last 15 years."
Asio - Australia's domestic security agency - increased the National Terrorism Public Alert Level from medium to high in September last year. This signifies that an attack is "likely".
Mr Lewis said this had been reviewed following the Paris attacks but that there were no plans to move it to the highest level of "extreme" which indicates an attack is imminent.
"If you consider there have been three successful attacks in Australia since that time, then I think that the threat level of 'likely' is most appropriate.
"We have no specific information leading us to believe there is any imminent threat of an attack presently, it is not appropriate for us to move the threat level to the next elevated position.
"This is very important for Australians to realise, we have no specific information about any particular attack planning in this country that would be reflective of what happened in France," he said.
In October. 15-year-old Muslim boy Farhad Jabar shot dead New South Wales police worker Curtis Cheng as the accountant left a police building in the Sydney suburb of Parramatta.
This came after the Sydney siege incident in December last year in which two hostages were killed, and the shooting of an 18-year-old man in Victoria who wounded counter-terrorism officers outside a police station.
Australia is part of a US-led coalition bombing IS positions in Iraq and Syria and has sent soldiers to help train members of the Iraqi national army.
Campaigners have accused a health board of risking patient safety and failing to learn lessons from a mental health ward scandal.
[NEXT_CONCEPT]
Australia's top spy has said there is no evidence of large-scale militant attacks planned against the country.