Update: If you get "ERROR: Could not start service com.apple.syslog_relay." you might need to change the rights to lockdown by doing
sudo chmod 777 /var/db/lockdown
It seems impossible to debug a packaged .ipa and understand why it's crashing. But unknown to most, iOS provides access to its system logs.
To debug a packaged app you will need
idevicesyslog a command line tool which is part of the amazing libimobiledevice project.
What's so great about this project is that this library is also available in linux and gives you easy access to the intricates of your iOS device.
To install it simply use the appropriate package:
# For OSX brew install libimobiledevice # For Ubuntu sudo apt-get install libimobiledevice
Then plugin your device, run
idevicesyslog and enjoy reading crash reports :)
Another command line tool made available by this library is
idevicecrashreport <Path_to_dump_folder>. Which will extract and dump the device crash logs in the specified folder.