Southwest Airlines, which canceled thousands of flights last week and angered passengers, said Tuesday it was making «solid progress» processing refunds, even as another issue caused more travel problems.

Multiple people tweeted Tuesday the crews said to them the planes could not take off because the weather system was not working or they lacked the necessary weather information.

The reports of delays on Tuesday came just days after the airline said it had resumed normal operations following the holiday travel chaos.

Southwest said in a statement late Tuesday that third-party provider IBM «experienced a brief outage in its service that provides weather data before Southwest dispatches flights.»

Southwest apologized to customers, saying in the statement that it anticipated «only minor delays» for the remainder of the night.

«We apologize for any inconvenience and appreciate everyone’s patience as we work to get Customers to their destinations safely and as quickly as possible,» the statement said.

The Federal Aviation Administration declined to comment, saying it was an airline matter. IBM did not immediately respond to a request for comment early Wednesday.

The FlightAware flight tracking website it showed 138 Southwest cancellations, or 3%, and about 1,560 delays on Tuesday. There were 24 Southwest cancellations and 115 delays for Wednesday, according to the website.

The latest delays came after the Dallas-based airline, which canceled two-thirds of its daily flights for most of the week before New Year’s Day, said Friday that normal operations had resumed.

All carriers were affected by a major winter storm that affected most of the US before Christmas weekend, but other carriers recovered.

Southwest canceled thousands of flights, stranding passengers and their luggage and sparking what has been called a meltdown that angered travelers.

The US Department of Transportation called it «unacceptable» and vowed to hold Southwest accountable. Transportation Secretary Pete Buttigieg said the collapse was a failure of Southwest’s systems.

Southwest’s chief executive has promised technology investments, which he said were already underway.

Earlier Tuesday, the airline said in a statement that it was working to win back the trust of its customers. southwest said it had made «solid progress» in rectifying problems caused to passengers, including in processing refund requests and reuniting travelers with their lost baggage.

White House press secretary Karine Jean-Pierre said Tuesday that «Southwest Airlines failed its customers, utterly.»

She said that customers must be reimbursed and reunited with their luggage.

“The Department of Transportation is watching. They are monitoring this very, very closely to make sure all of this happens and will seek fines from Southwest if it doesn’t cover a cost,» Jean-Pierre said.

emma li Y Suzanne Ciechalski contributed.