I couldnt help but notice that most of these dates coincided with storms or very windy conditions:
5th october - Cyclone Xavier
12th october - Hurricane Ophelia
16th october - Hurricane Ophelia
21st october - Storm Brian
27th November - gale force winds
24th December - record wind penetration on the grid
3rd January - Storm Eleanor
17th January - Storm Fionn
It appears that as very high amounts of wind generation is allowed into the grid, the frequency can drop to a dangerously low level.
One of our key tasks is to maintain balance between electricity supply and electricity demand. Electrical frequency is the measure of balance between supply and demand. When supply and demand are balanced, the electrical frequency is at 50 Hz. We must maintain this balance on the system all day, every day. The normal operational frequency range is 49.8 Hz to 50.2 Hz [Eirgrid].
You can see from the above diagram that the frequency has dropped below 49.8Hz on a few occasions over this period. As a result, the power station tripped and went offline. This then results in the frequency falling even further. At this stage, cutting demand is one of the few options open to the grid operator. This may explain some of the blackouts on these days.