I have been able to reliably get the springboard cache cleared for testing launch image changes by doing this:
- Delete your app from the device
- Power down the device
- Power up device, install and launch app.
The image updates properly every time. Shame I need to power down the device to get it to go – but at least I have been able to make progress this way. I hope this helps someone.
In case of the simulator, just restarting of simulator should work.