Crashing after lightweight Core Data migration - ios

Question

I am trying to master Code Data migration, its going to be important for supporting my app. The reason I need the migration is to preserve data. My app is used for psychological research and collection reaction time data. I have a game session and every game session has ordered set of moves. Every move has some properties. One of this properties is interval: Date. In the store version 1 it was named date and in the version 2 I renamed it to the interval and changed property's model version identifier to date.
App is not crashing on startup but when I am trying to view my old logs it crashes. I have UITextView and I display all my logs like this:
textView.text = "Interval = \(move.interval)"
If I create new game session and will view its log - the app works.
What is the best way to protect my users? Should I add additional logic inside my app for this? How can I display the old data after property was renamed?
Update:
There's no messages in the console, the app stops working with the line of code for updating the UITextView, it is highlighted in green with error message:
Thread 1: EXC_BAD_ACCESS (code=1, address=0x0)

Answer 1

I tried again from scratch and instead of renaming the variable, I created new one. This time app didn't crashed. I am sorry it is not real answer but it helped me to move on.
Lessons I learned:
Do not confuse Core Data Model Identifier in Xcode inspector and renaming ID. There's one model identifier (I left it empty) and renaming ID for every property.
If you have Core Data generated class with NSNumber, do not try to display them in console like this: label.text = "number = \(object.number)"
Do it like this:
label.text = "number = \(object.number.integerValue)"
This one gave me the same crash message, however it is not a problem if you're using NSDate.
I still have a problem when renaming variable. When I applied my commit again today I am getting the crash right on the start with the Can't find model for source store message. App in the simulator changed, so it looks like I can't reproduce this problem any more and instead have a new one.
Update
I had more practice and I think I was able to fix the crash described above.
I added next data model version - version 3 and introduced new variable. I did it like before, with switching current version from 2 to 3. Then app started to crash on launch with Can't find model for source store. I noticed that when I'm removing introduced variable the app is not crashing. I figure out that my Core Data couldn't migrate to version 3 because it already was on version 3:
I changed version from 2 to 3. I didn't change Core Data model.
I changed my code, fixed some bugs unrelated to Core Data.
Built and ran the project in the simulator. Note, now the app in the simulator has data version 3.
Changed Core Data model, built on simulator. It crashed after this step.
What I did to fix this:
Delete introduced variable. You can live generated classes as it is.
Change current version to previous. In my case, from 2 to 3.
Run the app and quit it.
Change Core Data current version and add new variable.
Run the app — it works.
Update 2
I met with this problem again and my answer didn't helped. Still, event after everything I described above.
I found this answer which this time finally fixed the issue. The secret was that new attributes should not be optional and they should have default values.