China does not want the problem solved

Reuters:

"The key to solving the nuclear issue on the peninsula does not lie in the hands of the Chinese side," Wang told the 15-member council in remarks contradicting the White House belief that it does wield significant influence. The ministerial meeting of the council, chaired by Tillerson, exposed old divisions between the United States and China on how to deal with North Korea. China wants talks first and action later, while the United States wants North Korea to curtail its nuclear program before such talks start. "It is necessary to put aside the debate over who should take the first step and stop arguing who is right and who is wrong," Wang told the council. "Now is the time to seriously consider resuming talks." Tillerson responded: "We will not negotiate our way back to the negotiating table with North Korea, we will not reward their violations of past resolutions, we will not reward their bad behavior with talks."

North Korea is a proxy for war against the USA.  The Cinese position has always favored North Korea's nuclear development.