Seems like there is a problem with using API ShiftReg_WriteRegValue(); and problem is being discussed with experts..
Instead of above function ShiftReg_WriteData(); API can be used.
Once you start the component please do not forget to give a clock to the component or else component may not work as required. One clock is required to start the logic in the component. It is as well mentioned in the data sheet.
Use the API , load the value into register(loading also requires a clock)
On providing the clock the data will be available at the output and the bit value will be held.