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."
Campaigners have accused a health board of risking patient safety and failing to learn lessons from a mental health ward scandal.