Crashlytics is not sending Crash report from iPhone

Xcode debugger does NOT allow Crashlytics to process crash reports. Yeah, that seem weird even to me when I read that first time but it is a fact (Source). That's is the reason we never see crash report When:
- running app in Simulator
- running app on iDevice by directly build and run from Xcode with debugger on.

To make sure a crash is reported during your testing (copied from Crashlytics support site):
1. Launch simulator
2. Press stop
3. Launch your app and force a crash
4. Relaunch the app from simulator
5. See the crash report in the web dashboard.

EDIT:

Added a reference; Crashlytics also provides a short article on a quick way to force a crash.

My be it's late but work 100%

Make some changes in project build settings like in below image

and follow these instructions.

The primary reason any crash reporter won't work on iOS is due to interference from different crash reporters. However, with Crashlytics specifically there could be something specific to them causing the crash report not getting reported.

Xcode debugger does NOT allow Any Crash Reporter to process crash reports. This is because XCode overrides any hooks into the crash handling call backs. This only happens when:

• running app in Simulator (with debugger on)
• running app on iDevice by directly build and run from Xcode with debugger on.

To make sure a crash is reported during your testing (http://support.crashlytics.com/knowledgebase/articles/92523-why-can-t-i-have-xcode-connected-):

1. Launch simulator
2. Press stop
3. Launch your app and force a crash
4. Relaunch the app from simulator
5. See the crash report in the web dashboard.

While a super old video it's still relevant, here's a video of the steps above (example from Crittercism): https://www.youtube.com/watch?v=sU6Su3PBFH4