You may check the location service and WiFi setting on your phone. It's important that both GPS and Wifi(even if they are not connected) are activated on your phone.
Please note that accuracy depends on many factors, such as your environment and your phone. There is moments when the highest accuracy will not be available(underground for example). The notification can be delayed up to 15 minutes which is depends on battery status or signal strength.
Please refer the below instruction for the detail.
- Check the location settings(GPS) and Wi-Fi
- Check whether place is registered correctly (if the range of notification is too small, need to increase more than 1 mile)
- iSharing > Menu(top left) > Place notification > select a friend > select a place > adjust range > save
- [iPhone only]
- Go to Settings > Notifications > make sure that iSharing is activated