This is because the contents of the Special pages are cached. Since there were issues after your import where the categories appeared missing, it was cached this way. So this is actually working as designed.
The cache should update over time, as users visit the pages, or new edits are made. You can force an update sooner (but still not immediately, we found that immediate cache rebuilds crashed people's servers), by going to AdminCP > VaultWiki > Wiki Maintenance Tools > Clean Article Post Cache.