By Andrea Lucia

DALLAS (CBSDFW.COM) – Dallas-based Southwest Airlines is apologizing to customers, after cancelling more than a thousand flights and delaying even more.

The airline cancelled more flights on Sunday and Monday than any other airline in the world, leading to speculation about the cause.

Calls to Southwest Airlines, its unions, the FAA, and local airports turned up no clear explanation for why Southwest was experiencing far worse problems than other national airlines.

In a new statement Monday, the airline pointed to “weather and external constraints, which left aircraft and crews out of pre-planned positions”, a problem it said stretched through the weekend and into Monday.

“Friday, there was an air traffic control issue in Jacksonville, which does a lot of the traffic control for the southeast United States, but they were only offline for a couple hours,” said Clint Henderson, senior news editor for The Points Guy. “But there was also weather going on in Florida. Southwest…they are staffed at the bare minimum right now. They don’t have a lot of padding. So when these things start happening, there’s a domino effect at times and it turns into a cascading failure.”

Henderson, though, believes there may be more to the story.

“Something’s not adding up. Because none of the other airlines operating in Florida have had the same issues that Southwest has had, he said.

Seen reflected through a double window, a Southwest Airlines airplane taxies from a gate at Baltimore Washington International Thurgood Marshall Airport on October 11, 2021 in Baltimore, Maryland. (Photo by Kevin Dietsch/Getty Images)

The airline and its union have adamantly denied widespread rumors circulating on social media of pilots calling in sick to protest the airlines decision to enact a vaccine mandate.

“I can say with certainty that there are no work slowdowns or sickouts either related to the recent mandatory vaccine mandate or otherwise,” read a statement from the Southwest Airlines Pilots Association’s leadership.

“It may not be a sickout, but the timing is raising questions, because Southwest’s union sued the government last week over the vaccine mandate,” said Henderson.

The union said it would be meeting with the airline Monday afternoon to discuss pilots’ concerns. “What was a minor temporary event for other carriers devastated Southwest Airlines because our operation has become brittle and subject to massive failures under the slightest pressure,” it wrote.

Jace Newman, a student at Tarleton State University, was getting ready for his flight back from Raleigh Sunday morning, when he says he got a text from Southwest telling him his flight to Love Field it’d been delayed by two days.

“I sat on hold for Southwest for about an hour and at that point I basically said, alright, if I’m having these issues, probably everybody else and their aunt and their dog is trying to get a hold of Southwest also,” he said.

He ended up spending $500 to book a flight for Monday on a different airline out of a different airport. Along the way, he met others in the same predicament.

“I’m glad all I missed was class,” he said. “I can’t imagine how many funerals were missed, how many weddings were missed, how many births were missed.”

Southwest reports the situation is starting to improve, but if you’re planning to fly the airline in the next couple days, Henderson suggests you may want to have a backup plan.

“Because remember all these passengers whose flights were cancelled will have to be placed on future Southwest flights, so it’s going to be a mess probably through this week,” he said.

A Love Field spokesperson said the airport kept its terminal open overnight through the weekend and would likely do so Monday night as well. It also planned to keep concessions open as late as possible for stranded passengers.