We recently had an order returned to sender because the automatic USPS validation removed the third address line with the box number. The recipient does not have street delivery despite her address being in the USPS validation system.
If the system had validated the street address and left the third line with Box number on the label, we would not have lost money on the return to sender.
Given that shippers choose between street and box delivery based on UPS vs USPS cost, it is essential that Shipstation does not remove the critical third line should the street address not be serviced by USPS, necessitating box delivery.
There is no harm from having an addition line including the box, but much needless cost and time wasted by removing the box number.