This post is about my Stack Overflow answer.
In Xcode, Window->Devices, choosing a device and clicking the up arrow in the bottom bar brings up the console and this traditionally allowed you to view output from your app when not running in the debugger, e.g. for testing background launching behaviour. Unfortunately as of Xcode 8 and iOS 10 there is now a lot more log output – very low level debug logging is on so hundreds of lines pass by every second, making it impossible to see the logs you are interested in.
The solution is to upgrade to macOS Sierra, the new Console app now displays connected devices, and it allows filtering the log by many different categories, process is probably the most handy where you can simply enter the name of your app’s executable. This now makes the Xcode Devices log redundant, it never was very good at search anyway.