Alaska Airlines warned of more flight disruptions on Monday after an unexpected failure of a critical piece of hardware at its data centers late Sunday forced it to halt all flights for about three hours.

Flights were grounded at 8 p.m. PT on July 20 after the outage. Alaska Airlines said a “critical piece of multi-redundant hardware,” which was manufactured by a third party, suddenly failed. The unexpected failure affected the airlines’ systems, requiring the ground stop. The stop was lifted at 11 p.m. PT, Sunday.

Alaska Airlines stated that the IT outage resulted in a “temporary, system-wide ground stop for Alaska Airlines and Horizon Air flights” around 11 p.m. ET and lasted until 2 a.m. Monday, the airline wrote in a statement on X.