Given the glowing results, the vast majority of companies that tried a shorter workweek stuck with the plan. But telecom company Magyar Telekom is one glaring exception. 

The Budapest-based company, which is the Hungarian arm of behemoth Deutsche Telekom that has a market cap of nearly $120 billion, piloted the program in June 2022 with no reduction in pay or people’s responsibilities—as is typically the case with other four-day workweek trials. 

There were benefits to start. But, the company says, it discovered through surveys and interviews with employees over the one-and-a-half-year period, that the initial efficiency rewards eventually waned. In addition, the benefits of the system didn’t apply uniformly to all employees, Magyar Telekom says.

“While some of the colleagues solved the tasks without any obstacles during the more intensive four days, it became clear that the majority of them could not work efficiently in this model,” the Deutsche Telekom–owned company said in an official .

300 employees

Magyar Telekom’s goal was to collect data and test how a shorter week would pan out, and a total of 300 employees in departments from customer service to sales participated in the Hungarian company’s four-day workweek experiment.

“We are constantly looking for new directions, how we can find better and more efficient solutions, whether it is about serving our customers or organizing our work processes. We attempted the latter by testing the four-day workweek, which I think shows the extraordinary openness of our organization,” Magyar Telekom CEO Tibor Rékasi said, adding that the company gained feedback and knowledge from the process, but will be pivoting to a standard workweek from March.  

“In light of the results, we shall continue to work according to the traditional work schedule, but going forward we look for new solutions that support work-life balance and the satisfaction of colleagues,” Rékasi said. 

Magyar Telekom provided Fortune with the company’s press release from Tuesday when approached for comment, and representatives at Deutsche Telekom didn’t immediately return Fortune’s request for comment.

Four-day workweek adoption elsewhere 

Companies in past trials that are in the minority of those who rolled back their five-day weeks have raised concerns about not being able to afford an extra day off, staffers having to cram their days with excessive workload, and potentially higher costs. 

Despite the few instances of companies falling off the wagon with the four-day workweek, a number of countries are still flocking to try the system given all the advantages it offers.

Germany, home to Deutsche Telekom, recently kicked off its six-month pilot of a shorter workweek with 45 participating companies. 

The program, as described by Dale Whelehan, the chief of 4 Day Week Global, the New Zealand nonprofit leading the pilot, is designed to follow a 100:80:100 rule whereby companies maintain 100% of pay for employees, who will work 80% of the time but achieve 100% of the output. 

“This is essentially a human resource transformation project, and it is a productivity intervention. Organizations are really struggling to grapple with improving their productivity or output of their businesses’ performance—that’s because they’re fundamentally missing the foundation of a business which is run by its people,” Whelehan told Fortune last month.

For its part, the four-day workweek movement has had a few landmark wins in recent months—German IG Metall, which is Europe’s largest industrial union, managed to negotiate standard working hours to 32 a week, roughly panning out to four days. In December, luxury sports-car maker Lamborghini said its production workers would have a shorter week.