We took a look at the Americommerce support docs and it looks like it might have to do with how the columns were mapped in their system for export. Here’s the page from Americommerce's documentation on exporting under ‘Export column mapping’: https://support.americommerce.
In addition to that, there's a check box to export items on separate lines which should be checked.
Feel free to reach out to support@orderimp.com if you still need additional help!