Hi, Yipin,
I do not expect disconnection of the exposed GND will change the input impedance too much, but I am not very sure. You probably need to check the whether each pin is soldered down well. Also, if you find return loss does not satisfy your requirement, extra matching network might be needed at the RF port for a specific frequency range of interest. You could follow the instructions in the datasheet on page 15.
Peng