If this was imported during your last test import, then I'm not aware of any changes that would prevent this from being imported this time, unless the source forum itself has changed.
Even if the forum was set with Display Order 0, it should still appear in the Admin Panel under Structures > Area Manager, after importing. It should be near the top of the list.
If it was not imported, was the source node actually set as a wiki forum, using either "Wiki" mode or "Island" mode?
If it used "Wiki" mode, was it a namespace or did it fall under another namespace? Completely un-namespaced "Wiki" modes would have been corrupt and could not be successfully imported.