Were these threads imported? If so, rebuilding the thread information may solve it.
Alternatively, it sounds like data may have actually disappeared. This could be from data corruption or restoration of an inconsistent backup. Unfortunately, if that's the case, there isn't much that can be done.
Otherwise, if the counts are simply wrong, rebuilding the thread information should sort the counts.
If rebuilding thread info doesn't fix it--try rebuilding the post position counters with it--then it sounds like it could be a problem from the import. It does sound like a redirect being brought across, which would explain the lack of content. This would only happen if it weren't tagged as a redirect in the expected way.
You'd just need to (permanently) delete the thread via the inline moderation tools.