Hello,
It seems, you are testing with production TO. you have to maintain a specific entry. that means,
WH ST1 914 Desired Printer.
WH ST2 914 Desired Printer.
WH ST1 916 Desired Printer.
WH ST2 916 Desired Printer.
Here, Assign the printer based on ST1 & ST2. Then, It works fine.
Regards,
Sathish