Problem

After upgrading Magento to version 1.9.3.0 or above, orders in Extensiv Integration Manager no longer contain any products. The inventory sync may have stopped working as well.

Solution

This is caused by a bug in Magento. There are currently two options you have available:

1. Upgrade the version of PHP on your Magento server to PHP 7 or above
2. Make changes to the Magento code on the server, by following these directions: http://magento.stackexchange.com/a/140784/15231