So to sum it up long story short, he lied about his age 3 or 4 times, did CA, was being a total a-hole in general throughout the whole show even to the contestants. He even fatshamed other contestants (with bad intention ofc as he got angry when another contestant Hikari was telling him some sort of joke that was never that serious and then KSoul himself got angry about it and started calling him names and mocking his weight). KSoul used to be at another survival show in 2020 but in that show he showed no motivation or desire to improve or work more on his skills (I assume? since they were in the practice room) and would blame his group mates instead and then left the practice room while being upset.
Btw I have not watched the show at all but I have came across numerous threads and some clips that reveal a lot about his behaviour in general and throughout the whole show.
i can link you the threads that sum up all the controversies that he has done if you like. So yea that’s basically it.