Although we use one of the fastest and most reliable hosting services available, there was an incident recently which caused a loss of some data. We are still working with the provider to understand and avoid this issue in the future, but we have corrected the immediate problem.
Please go to Settings > Data Cache > Check for Updates to get the latest and complete maps data. Note this will cause a full download of all maps and other data needed for all cities, regions, countries, routes & tracks that you have marked with a green (or yellow) star. It is recommended you do this while on a WiFi connection.
I just verified again that the current datasets are complete, and also tried downloading NZ myself, and it completed without problem.
If you go to Check for Updates, does it tell you that you are already up to date? Also do you have Wikipedia enabled, and if so in which language? I only verified the map data and english wikipedia so far, so am wondering if there could still be missing wiki articles in another language that is causing this problem…