A “hot vax summer” is turning into more of a “hot mess” for airlines coping with behind-the-scenes operational issues.

Spirit Airlines canceled hundreds more flights Wednesday as the airline grapples with an IT outage, bad weather, worker shortages and peak-summer demand, a company spokesman told NBC News.

By 11 a.m., Spirit had canceled 49 percent of its flights, according to airline tracker site FlightAware, a total of 341 flights. It’s the fourth consecutive day the carrier has had widespread operational difficulties.

In an emailed statement, company spokesman Erik Hofmeyer cited “overlapping operational challenges including weather, system outages and staffing shortages” for the “proactive cancellations.”

An IT outage, the second in two days, took out the company’s worker-scheduling system Tuesday, preventing management from accessing schedules or making crew changes, according to a statement from the Association of Flight Attendants-CWA union. Hofmeyer confirmed this was one of the airline’s operational difficulties.

Customers took their complaints to social media. Videos show hundreds of Spirit Airlines passengers stranded in airports in Puerto Rico and Las Vegas and a pile of unclaimed luggage roped off in Orlando, Florida.

“Thanks for cancelling my flight and then providing a $50 voucher as if that takes care of this craziness you have put us through,” one flyer tweeted.

“shoutout to @United for coming thru when @SpiritAirlines decided to cancel my flight an hour before takeoff and offer NOTHING to help me get another flight,” another tweeted. “i swear i will walk barefoot on broken glass from coast to coast before ever booking with Spirit again.”

Over 2.2 million passengers flew Sunday, three times the number a year ago, according to checkpoint data from the Transportation Security Administration.

Airlines took aggressive moves to cut overhead when the pandemic hit and sharply curtailed all but essential travel, but experts say they overshot the mark.

“Part of the key to airlines generating cash has been for airlines to 'wax optimistic,' talk their book by aggressively publishing expanded schedules, flights and capacity, and selling tickets long in advance,” said Bob Mann, industry analyst with R.W. Mann & Co., an aviation sector consulting firm, in an email. “Actually having to provide the transportation has in a few percent of cases (but for many flights and many, many customers) become unrealistic with resources actually available in the moment.”

“Some airlines now have several days' worth of interrupted passengers vying for the few empty seats on peak period schedules, which will be uncomfortable for airlines and passengers to resolve,” he added.

All of this comes after the airline industry received $48 billion in payroll support from coronavirus relief legislation.

American Airlines also experienced hundreds of cancellations and delays Sunday and Monday as “heavy rain, strong winds, lightning, microbursts and hail” hit the airline’s Dallas-Fort Worth hub in Texas, the carrier’s largest, spokesman Curtis Blessing said in an email. By Wednesday the cancellations had fallen to just 3 percent, according to FlightAware.

One factor exacerbating problems is the issue of booking hotels for crew during layovers, American Airlines pilots and flight attendant unions said in a grievance filed with the airline last week.

“We have Flight Attendants sleeping in airports and outside of baggage claim due to the company not providing hotel accommodations in a timely manner,” said Julie Hedrick, national president of the Association of Professional Flight Attendants labor union, in a statement.

American Airlines crews said that behind the scenes the airline has cut costs and can’t handle the demand.

“They furloughed way too many pilots and gave out too many leaves to flight attendants and pilots,” said one American Airlines crew member, who requested anonymity out of fear of reprisal from management. “They reinstated way too many flights without realizing and underestimating their staffing.”

Crews are reluctant to pick up some flights, despite extra pay being offered, because of the issues booking hotels, the American crew member said. They said this stems from outsourcing hotel operations to a third-party provider.

“This is a short cut for the Company to save money while not guaranteeing [joint collective bargaining agreement] compliant hotels for our crews,” the pilots union said in 2019 statement preceding a test run of the system.

"Taking care of our crew members while they are away from home is a priority for American," Blessing said. "We are looking into the concerns raised by APA and APFA," the spokesman said, referring to the pilots and flight attendants unions.