Electricity is pulsing through Spain and Portugal again after a massive outage knocked out power in both countries on Monday. So too are questions.

Electricity was restored to almost all of Spain and Portugal on Tuesday morning following a massive power cut affecting the entire Iberian Peninsula, but the cause of the blackouts remained a mystery.

That conclusion has been supported by the operator of Spain’s national grid, Red Eléctrica, which has located where outages began on Monday. Two separate incidents of power outages led to instability in the grid leading to a “breakdown in interconnections with France,” leaving the Iberian grid isolated.