Probably just the number of cycles/hours between maintainence required for ETOPS approval. Bordeaux does the scheduled maintainence, so EI probably either kept it on the Atlantic for a week non ETOPs as prior planned, or perhaps the number of diversions/returns to base/hours clocked up exceeded what they'd planned for before the next maintencence was scheduled and had to operate it non-etops.
In other news: Large numbers or new routes and increased frequencies next Summer from EI.
Aer Lingus announces new routes at Dublin and Shannon | Irish Examiner