UPDATE: Southwest Flight through Nashville appear to be suffering numerous delays and cancellations.  Southwest Airlines was the only airline to report the issues on that scale. Click here to check your flight status at BNA.

CHICAGO (NewsNation Now) — Southwest Airlines has canceled or delayed thousands of flights, leaving customers stranded after a weekend plagued with major service disruptions.

More than 1,900 flights were canceled by the airline over the weekend, according to the online tracker FlightAware. The Dallas-based airline blamed air traffic control issues and bad weather for weekend “operational challenges” that resulted in the cancellations.

By late morning Monday, Southwest had canceled about 365 flights — 10% of its schedule for the day — and more than 600 others were delayed.

Southwest cancels thousands of flights nationwide, blames woes on air traffic control issues and weather
But what exactly is going on? Why did one of the nation’s biggest airlines face such major delays, stranding millions? Here’s what we know:

WHAT IS SOUTHWEST SAYING ABOUT THE CANCELLATIONS?
Southwest has blamed air traffic control issues and bad weather for the “operational challenges” that resulted in the weekend cancellations.

Southwest issued a statement to NewsNation on Monday morning, saying that while the flight schedule was “closer to normal,” they were still navigating new weather and the repercussions of the weekend flight disruptions.

“We have a closer to normal operation today, navigating some new weather across our system. The weekend challenges were not a result of Employee demonstrations. To recap the weekend cancellations, the bad weather and ATC issues in Florida, a large operation for us, on Friday night created significant flight disruptions throughout our network and we spent the weekend working to recover from the high number of displaced Crews and aircraft. Although we have some new weather in parts of our system, today’s operation has vastly improved from the weekend, with a much smaller number of cancellations linked to our weekend recovery efforts. We appreciate our Customer and Employee patience as we worked to reset our schedule.

WHAT IS THE FEDERAL AVIATION ADMINISTRATION SAYING?
The FAA, which provides air traffic control services, took the unusual step of pushing back against Southwest’s explanation.The FAA said no air traffic staffing shortages had been reported since Friday but that some airlines were experiencing scheduling challenges due to aircraft and crews being out of place.

HAVE COVID-19 VACCINATION POLICIES PLAYED A ROLE?
Southwest announced last week that its employees must be fully vaccinated by Dec. 8 to keep their jobs. Workers can ask to skip the shots for medical or religious reasons.

Rumors circulated over the weekend that employees had staged a massive “sickout” in protest of Southwest’s new policy. Southwest disputed those rumors Monday morning.

Southwest had remained silent on the vaccination requirements even after President Joe Biden announced his vaccine mandate order for federal contractors and large employers. United Airlines was the first major U.S. carrier to announce a vaccination requirement in August.