Willem,
I was posting on an old thread that I started in an effort to get folks to continue posting on it and noticed after I submitted the reply....the pages that were missing repopulated and the content restored.
I tried it on other threads that were from the time frame affected by the upgrade/content loss that I knew had a lot more posts than were showing and had the same thing happen and the missing content re-populated. I noticed I could do it with a single letter post then delete my post and the re-populated content remained.
Is it just me, and the content was there and some setting hid it on my end....or does this actually work and is there a faster way to do this to all the threads?