My App won't load on device

I am going through the checklist tutorial, which is great, my code has deviated from @hollance as I try new things. It compiles ok and I put it on my device fine, used it fine. When to either reopen it or take it out of suspension and it just flicks as if to open and then closes and I can’t get it to appear. I’ve deleted the app and reloaded it onto the phone twice.

As I’m pretty new to iOS I’m not sure how to debug something like this or likely causes?

Do you know how to use Instruments?

What about the console debugger window?

Does it also do this on the simulator?

I realized this was my fault, I never put the app into suspension on the simulator so when it awakened that’s when I got the found nil unwrapping optional. So I was able to fix this by deleting my app with the old plist in.