Residents at a Health Service Executive-run nursing home in the northwest had "unexplained bruises" during a recent inspection by the Health Information and Quality Authority (HIQA).
Oversight arrangements at the home failed to identify unknown bruising and peer-to-peer incidents, according to HIQA.
The findings are included in one of 50 nursing home inspection reports published by the independent watchdog.
Inspectors found that not all residents living in the designated centre experienced a good quality of life and "incidents" were not appropriately managed in line with safeguarding policy.
Three safeguarding incidents were not notified to HIQA's Chief Inspector, including an allegation of financial abuse and the unauthorised access of a member of the public into the designated centre.
There were also incidents of physical aggression between residents, according to the report, which showed "clear safeguarding risks".
The inspector found that a number of residents with acquired brain injury were not sufficiently supported to participate in activities in accordance with their interests and capabilities.
The registered provider confirmed that they were liaising with community services in order to reinstate these services for the residents.
The impact of staff shortages is evident throughout many of the reports published by HIQA.
There was evidence at one nursing home, south of Dublin, that call bells went unanswered for long periods of time.
Due to staff shortages, the company director had stepped into the role of Person in Charge following the departure of the previous Person in Charge.
HIQA was told that this was a temporary arrangement following "an unsuccessful recruitment campaign to fill the vacant post".
At another centre, also located on the east coast, north of Dublin, staff shortages resulted in the person in charge working as a staff nurse.
It meant that she was unable to provide appropriate staff supervision, leadership and guidance required for effective service oversight.
This provider had a good regulatory compliance history, but had "depleted governance structures, inadequate resources and a lack of service oversight" which led to a deterioration in the service provided.
The HSE says it has taken a number of actions to ensure full regulatory compliance.
In a statement, it said all incidents of bruising would continue to be reported on the National Incident Management system and a medical officer would continue to review all incidents and accidents within the centre, to ensure the welfare of the residents affected.
It said all incident forms had the "required level of review and depth of analysis to determine the root cause" since January.
Where a root cause is not determined, "it will be managed in line with the designated centres safeguarding and protection policy as appropriate".
Risk management policy at the centre was reviewed and was updated in February, according to the HSE, which has required the use of a body chart to record incidents of unknown origin.
"Unfortunately there is no way to prevent people from experiencing minor bruises and scratches in any engaged lifestyle," it said.
"The Designated Centre supports residents to express their will and preference and their ability to make choices and self-determine", it added/
The statement said the designated centre would continue to support residents "to positively risk take" whilst at the same time being mindful of risk assessment.
"The HSE will continue to work to ensure that a high quality of service is maintained within this centre," it concluded.
