The finding comes weeks after the federal agency threatened to cut off $400 million in annual funding after determining that Parkland jeopardized another patient, according to the Dallas Morning News.
Parkland previously adopted hundreds of safety reforms to avoid further federal scrutiny.
Parkland CEO Fred Cerise on Wednesday acknowledged failures in a nurse's supervision of the patient in June.
"There are initiatives we're pursuing to improve the situation," he said, adding that the hospital is being responsive to federal calls for ongoing reforms.
New education and training for staff could be part of the hospital's official response in the coming days to the CMS, Parkland administrators say.
Parkland had been under nearly two years of on-site scrutiny by federal authorities after they had found dangerous conditions for patients in various hospital departments. Authorities found in February that Parkland psych staffers gagged a patient with a toilet paper roll and covered her head with a sheet, leading to two firings and two resignations.
Officials with the state Department of Health Services said the recent care failures violate a separate settlement action that carried a $1 million fine against the hospital, the largest in state history.
"These are serious incidents," Carrie Williams, a spokeswoman for the health department, told the Morning News. "While Parkland has made significant progress, we don't stop regulating."