LT8311 operation with gate driver

 Hi, 

We are using LT8311 as sync rectifier controller of forwward converter.
When FG pin connected to forward FET, there is no issues.
But when CG pin connected to chatch FET, input current is increased and efficiency is goes down.
Is this light operation?

Wave forms are,
Upper : VDS of primary main switch
Middle : FG
Lower : CG