One of the spanish specialized media suggests a possibility:
That the crew wasn't initially aware of the damage because at first there wasn't such a hole and that only after climbing to higher altitude the pressure difference opened it up.
That is hard to believe if you look at the Avheralds report:
The airport reported two cabin crew received neck injuries (mainly bruises) from their seat belts as result of impact forces.
If the pilots didn't notice it themselves you would expect a call from the back.