A woman, Jennifer Campbell, passed away from pneumonia and sepsis after her medical notes, which referred her for further tests, were lost by the Betsi Cadwaladr University Health Board.
The senior coroner for north-west Wales expressed concerns that despite her previous warnings, no improvements had been made by the health board.
The coroner issued a prevention of future deaths report, and the health board has until December 19 to respond. The report noted that there was no formal investigation into how the referral was lost, and no audit had taken place to check for other lost referrals.
The coroner emphasized the importance of addressing such issues promptly to prevent risks to patients.