Did you put nwiki in your 1.9 build before running the upgrade? If you don't do that, then the standard wiki will over-write your nwiki tables, and the data will be lost.
To get them back, I think you would need to revert to your 1.8.4 database backup, replace the standard wiki with nwiki in your 1.9 build, and then re-run the upgrade.
We have however tried to restore backups of the courses that had those NWikis in a 1.8 test installation and we still can't recover all the wikis from the students. What we see is something that looks a little strange. We've been able to recover some of the wikis that the students had written (not all!) but they all appear as if they had been created by the course teacher. These were wikis that were created in the 'group mode' and that appeared correctly assigned to the different groups in the original 1.8.4 installation. Somehow now all the information about the groups that created them has disappeared. This is a disaster since we are in the middle of exam period and the teachers need to evaluate these wikis.
Standard wiki does NOT upgrade database since Oct 2006.... Are you sure that you can not replace NWiki in /mod and continue working??
I don't know what to tell you. I don't know what did it but the wikis (created with Nwiki) disappeared from that course when we upgraded to 1.9.
Would it help you figure out what is wrong if we gave you a backup copy of the course that contained the Nwikis made before we upgraded? As I told you, when we try to restore that course, we get some of the wikis but they all appear as if the course teacher had created them.
I can not assure you (I'm not in front of NWiki code) but I remember something like "if author doesn't exist, assign this page to teacher"
Send me your backups and I'll make some tests.
Mmm, but the author did exist. The course was upgraded with all the users in it (who were the authors of the wiki).
Something is definitely wrong with the upgrade. I have logged in as a student and I notice that students cannot even see the 'edit' tab when they access the wiki.
I'll send you a private message with the link to the backup file. It's going to take me a while because it is a huge backup file and my bandwidth is slow for uploads.
I haven't forgot about you, I still waiting for the backup... Did you send me it?
It is very heavy (150 MB!!) I don't know how this course got to be so heavy) so I'll upload it to a server and send you a link.
did backup you send me caused restore problems? I have rebuilt your course and all your wikis are here.
All pages in backup file and their authors are matching correctly. I have counted 13 pages edited by yourself. Is it possible? Maybe the problem is in backup process, not in restore....
I had managed to restore the backup I sent you without any problems except that I didn't get 13 wikis. I got fewer wikis and all of them appeared as if they had been created by me. But I didn't edit any of the pages (except for maybe a title in the 'first page' of some of the wikis). The students wrote all the wikis.
I don't know whether the problem is in the backup or in the restore, really. If this had happened a few months ago, I would have thought that the problem didn't have to do with NWiki because we had some problems with our installation. But now everything is newly installed and we haven't had problems with anything else. Backups and restores are the weak point in Moodle or at least with respect to NWiki and perhaps other modules.
Do you have this restored course anywhere where it is accessible? If you do, send me a link via a private message. I'd like to see these 13 wikis and try to figure out who they belong to.