Found reason for app crashing (iOS version).
Over the last month the Solo App was crashing during flights and especially when using smart shorts.
I raised a support ticket with 3DR, but other people using the app didn't have the problems. So after several hours of trail & error, I found the reason and verified it with over 3 hours of flight without a app crash.
I was using the iOS app via SoloLink (Wi-Fi) to the controller & drone as standard, but I also connected an external GPS receiver (Garmin GLO) via Bluetooth.
But my iPhone 7 was also connecting to my iPad Mini 2 with internet connection via Bluetooth. On top of this I enable "Save Videos To Camera Roll", but I also have an iCloud account with the option to automatically save photos & video to the cloud. So the first few minutes of flight was OK until I started recording video & using the smart shots. The iPad was connecting to the internet via the Bluetooth (very slow connection) and was saving the videos to the cloud, and also trying to download satellite map data instead of using the cached map data, this was causing major problems with the Wi-Fi comms with the SoloLink and crashing the app.
So, if you have an iCloud account, disable the Settings > iCloud > Photos "Upload to My Photo Stream", and make sure your iPhone is not connecting via Bluetooth while flying.
I still have the minor issue the back arrow on the full GPS satellite map screen, but this is minor, just tap the small video screen.
I hope this info helps someone else, and I would like to thanks this community for all the help received.
May I be the first to wish this community a Merry Xmas & a happy new year 2017.
Be safe and happy landing.........................