Thousands of Southwest Airlines (LUV  ) passengers found themselves stranded in airports across the United States over the weekend and into Monday following the cancellations of countless flights.

The airline's issues began over the weekend, with Southwest delaying and canceling thousands of flights over the weekend and into Indigenous Peoples' Day, leaving many travelers attempting to rebook amid holiday festivities and related disruptions. Cancellations and delays tapered off through the three days, only canceling 2% of its scheduled flights as opposed to Sunday's 30%.

What went wrong to cause a major carrier to cancel over a quarter of its flights? Southwest tweeted that the disruptions had been caused by "flight delays & cancellations occurred for a few hours Friday p.m. due to widespread severe weather, military training, & limited staffing in one area of the Jacksonville en-route center" (a claim disputed by the FAA) Alternative theories range from a pilot protest in response to the airline's vaccine mandate to the Southwest over-extending itself.

The former has been disputed by the Southwest Airline Pilots Association (SWAPA), which has instead suggested that the problem lies with Southwest itself.

"SWA has claimed that the immediate causes of this weekend's meltdown were staffing at Jacksonville Center and weather in the southeast U.S., but 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," the Union wrote on Sunday , "Our operation and our frontline employees have endured continuous and unending disruptions since the first time our airline made headlines in early June due to widespread IT failures."

Given Southwest's many public follies over the last year alone, from the IT debacle mentioned by SWAPA to the company staring down a $3.9 million fine for improper pre-flight weight calculations, it would appear that the company's struggles are mainly internal. Given Southwest's decision to curtail its fall flight schedule, it can be assumed that the airline overextended itself and found its already strained workforce unable to carry the weight.

Southwest shares took a blow over the debacle, losing 3.5% in a pre-market drop on Monday. Shares slid a further 0.6% during trading on Monday but appeared to be in recovery on Tuesday, recovering 1% by 11 a.m.