Here is a corrected version of the Register Definitions with the full location of sw_op. 

Here is a corrected version of the Register Definitions with the full location of sw_op. 

When you power down the sensor's power by disconnecting VS through Q1, does the host's I2C lines stay high? 

When you disconnect I2C devices through switches to save power, it is best to disconnect the i2c lines as well. For example, the EFM32PG12 STK board (User Guide) has a Si7021 RHT sensor on the board. Figure 6.4 on page 15 shows how the Si7021 is schematically connected.