Unlocking my phone while the Minecraft app is on the "Generating world..." screen sometimes results in my phone completely locking up. It doesn't respond to screen taps, the Home button, or even the power button. Sometimes after a couple minutes the app crashes, and sometimes the entire phone crashes and reboots.

If it's relevant, I'm playing on my older iPhone 7 with 32GB of storage, which isn't a lot and there's not much spare space... around 2-3GB. 

Steps to reproduce:

1. Play in a local world. Open the menu and select Save & Quit.
2. Hit the phone's power/lock button during the "Generating World..." screen to turn off the screen while the Minecraft app is still active.
3. Some time later, unlock the phone using the Home button. 
4. App will appear locked and the phone will be unresponsive for at least 30 seconds.
5. App or phone will crash.

I'm not sure, but it seems to be worst if there are pending iOS banner notifications that pop up immediately upon unlocking the phone. This seemed to start happening after a fairly recent (last 3-6 months) iOS update, when the Messages app got more resource hungry.