I don't believe the cause is iOS. In that case MCPE starts from the home screen as though you've just launched the App. You can test for yourself, especially if you have an older device with 512mb RAM. Otherwise you'll have to launch another RAM heavy App straight after MCPE. You'll see MCPE will start back from the home screen when the iOS has cleared it from RAM.
In this case you return straight back into the hosted world, but get a message Server Restarted. And it happens even on an freshly rebooted iPhone 6s when all you launch is MCPE and go to home screen and back.
Sorry if its not clear. MCPE doesnt crash and iOS doesnt clear it.
The server just stops and disconnects everyone if you switch away from the app. It didn't used to do this before 0.14 which was better. Now if I'm running a server and get a message people who are connected get disconnected if I go to answer the message.