I don't think IA was the problem, it landed on time from Tenerife at midday which would have been after the departure time for the Cancun flight anyway. IE did have a divert to St. Johns a few days ago with residual delays since, IG also didn't move yesterday after arriving the day before (29th) into Manchester from PUJ so it would have likely been one of those two that IA was drafted in to cover for as soon as it was available.