Maps app on iPad-mini wifi only without internet
Make sure you enable WiFi all the time. Even if you don’t have cellular data or connected to Internet, the device can still estimate your location based on the surrounding WiFi source.

Update: Maps will use the surrounding WiFi (protected or not)  to pinpoint your position. That might explain why it only occasionally works. If your iPad can’t find any WiFi available, then your position can’t be estimated.