The Chess Dao's deduction was not omnipotent. It relied on using the "known" to calculate the "unknown," rather than relying on abstract and mystical fortune-telling. Therefore, while Chen Yi could figure out many things, there were just as many he couldn't predict.
For instance, Yan Fusha of the Five Poison Sect suddenly abducting Pei Guanli. Or "Jackal" Du Cang tracking his scent to the Xiao family's home and subsequently kidnapping Xiao Wan'er. Or Liu Hong setting up a grand scheme involving the disaster refugees.
Chen Yi could, at most, deduce that Liu Hong was plotting something major, but he couldn't figure out exactly what it was. He simply lacked the necessary clues.
