Yes, exactly, the data is as far as I know all there, and if you look at the history most of it has not been changed for years. So it's not an issue with the article texts themselves.
I at one point though it might be the templates, but from what I could tell, the templates had also not been changed, but that was a while ago when I looked, and I don't remember any specifics, and I might just be wrong on that point.
I've been working in IT for 35 years. These kinds of errors happen because something has been changed. Someone made a change in the the Wiki software, or a patch has broken something. But without access to the hosting server and the Web and Wiki installations, any speculation on specifics would be folly.