Well, I deduced that it was probably the article storage backend that would be causing those issues. But now, if you've changed it, and some of the articles still don't show up, then I'm not really sure what can be happening. Have you tried clearing OTRS's caches and/or restarting apache and/or mysql?
Again, I'll urge you to take a look at OTRS and Apache's log files while accessing one of the tickets that have issues. The log files may give some hints about what's going wrong.