Logging in today to check-in, it was very slow at first but then woke up. Whilst I have no doubt that rapid scaling is available - it depends how much they have signed up for. What we have seen over the last 10 years is that their system fails far more than it should and that, when there is an external problem (Volcano / ATC / etc.) they system struggles to deal with the load.
It is well understood that updating their system is horrendously expensive and will take a long time but they show no signs of starting. That is all on the table for IAG to fix.