Official comment
Not having the terrain downloaded for that area will cause issues in tagging. Are you downloading the terrain ahead of time by clicking 'Load Terrain' and then selecting areas you want to download? They should show as orange rectangles when the are cached. Once they are cached you should be able to operate at that location while offline.
Are you using a 3rd basemap URL for caching the basemap tiles?
What iOS version and iOS device type? We haven't updated Tag Pilot in a pretty long time.