First occasion was a fatality at Malahide.
Not sure about last night, it appears the 2315 special from Malahide to Connolly (an 8 car 29k stopping at all stations) had door problems at Portmarnock. A second train (a DART) left Malahide and was stranded in the section. The situation escalated as frustrated passengers in the reportedly heavily overcrowded trains disembarked onto the track.
The last Dundalk service was held at Clongriffin until around 0100 as was a special to Belfast. Services in both directions were stopped for between 90 and 120 minutes.
There were further delays at Donabate due to a medical issue on the Dundalk train. In typical Irish Rail fashion the Belfast train was held to follow the Dundalk local and apparently didn't reach Belfast until 0400.
A special DMU apparently ran from Connolly to Bray for passengers who missed the last southbound DART.