Yup. It was the US and its dogs that have discredited and hollowed the UN sanctions.Nice theory but let us wait and see what CN will do as North Korea is planning another nuclear test soon. When asked if China will support more sanctions if North Korea conducts another nuclear test, Zhao Lijian also implied that Beijing will not support new sanctions even if Pyongyang tests a nuclear weapon.
In addition to abusing the sanctions for covert purposes, the US also retreats from talks with NK to address its security concerns. The UN sanctions on NK have lost its purpose. Why would China support adding new sanctions if the existing ones are failing?
The US uses sanctions as weapons for regime change. When the US doing this with its own domestic laws, China cannot do much about it except retaliation. But if the US wants to force the UN to follow, China won't allow it to happen.
This is exactly the footgun I was talking about.