There are some. If we go to Reddit, they explain things better there.
The biggest one relates to the show's credibility. So, Jung Hae Min (the cyclist & runner up) was the actual winner of the show. But the production team forced the finalists do the match 3 times, because of technical issues (if I'm not mistaken, something wrong with the audio recording). Basically he already won the first 2, but the show said "nah", until the match fell to Woo Jin Yong's favor. News came around, especially Hae Min's social media distances himself with the show, and other contestants like the car dealer guy and Yun Sung Bin's coach also said it. The production team eventually denied that the competition is rigged, but recently Hae Min decided to do an interview to confirm everything. Not sure if it's against NDA, but according to his words, he doesn't exactly want any compensation, just wants to tell the truth. Overall, they didn't necessarily seem to intend on making Jin Yong the winner from the start, but it's more about being very unprofessional.
The other controversies are more about contestants' past. I don't think they should affect the program's future, but we're talking about South Korea, everyone's reputation is somehow involved in the brand image. So Kim Da Yong (the stuntwoman) was involved in bullying and assault when she was younger. The victims decided to speak up and Da Yong actually admitted (half of) it. And then Jang Seong Min (one of the rugby players in the show), assaulted his girlfriend with a weapon (that's all I know).
