The airline blamed air traffic control issues and weather in Florida on Friday, saying the ripple effects put planes and employees out of place, and it had too few reserves [!] to pick up the slack....Southwest and its pilots union have steadfastly denied that workers walked off the job to protest a federal vaccine mandate. (The pilots sued the airline to stop the mandate.)

"The fact is the Florida weather on Friday and unexpected ATC issues on Friday night resulted in delays and cancellations across our network, and it just got us behind."
[...]
"They were just caught in a perfect storm," [Jon Jager aviation analyst] said, citing staffing levels [!], weather and flight crews running out of time because of the delays and cancellations. Pilots and flight attendants are only allowed to work a certain number of hours per day due to [union] contract[s] and government rules.