UCC256302: About operation when load is added to output

Part Number:UCC256302

hello.

I made a prototype board using UCC 256302.
I turned on the power supply.
We output voltage as specified.

Setting the load at about 0.8 A will lower the output voltage.

I thought that the overcurrent protection circuit operation is taking place, I lowered the resistance of the ISNS pin, I tried lowering the capacitance of the shunt capacitor
But the situation did not change.

Please let me know what you think is the cause.

 Thank you.