I recommend running an import on a fresh WordPress installation. To do this, you can use the WordPress Database Reset plugin (https://wordpress.org/plugins/wordpress-database-reset/). This plugin can be used to remove all existing content and install a new version from scratch.
May I speak with your colleagues Luke? I have talked with him earlier and he knows better how to fix this issue without installing additional plugin. It would be appreciated if you can help me out with this issue asap