When printing multiple packing slips, render each packing slip one at a time.
When selecting multiple orders and then printing packing slips for those orders, ShipStation currently renders all of the HTML for all of the packing slips in one step to one PDF.
This fails when rendering multi-page orders if more than one order is rendered at a time. (Multi-page orders render perfectly when rendering one at a time.)
Best practice would be for ShipStation to render each packing slip one-at-a-time to a temporary PDF, and then join all of the rendered PDFs (one for each packing slip) to one joined PDF. That one joined PDF would then be printed / downloaded.
Rendering each packing slip to a temporary PDF would ensure that the HTML from one packing slip would not affect the rendering of any other packing slip. Currently, HTML from one packing slip can and sometimes does (in our case, when printing multi-page orders) affect the rendering of other packing slips.