Script only working 95% of the time

I have a custom suitescript created to automatically set the correct tax code for customers who are marked taxable (this is set so that if either the location or ship via change, the script is activated). I also have a suitescript that automatically sets the location if any of 3 customers are selected (we have a generic retail custom created for each of our three locations. When this customer is selected, we want the location to automatically change to the correct location).

The problem is happening on Cash Sales where the customer is any one of the three customers that the suitescript looks for to change the location. Most of the time the customer is selected, the location is changed, and the tax is corrected. But 5% of the time the location is changed and the tax goes blank. It also unchecks the taxable box.