I personally experienced the issue with 2.8.15, but it appears others are seeing the same problem even on version 3. Just now, I quickly took a look at the latest version 3 source code, and it is likely that the issue is still around. That is, I had identified the cause of the crash and we fixed it in our app.
The issue is presented when a user rapidly opens and closes InAppBrowser while using Cordova iOS application because (referring to the latest CDVInAppBrowser.m as of 10/3/2013 with commit hash of a001cffc30cf94cb406128f7b68d143e2cd62114) self.inAppBrowserViewController (line: 332) is nil if 'browserExit' (line: 353) is called before 'webViewDidFinishLoad' (line: 328) is invoked.
We put our own patch around line 332 as below, and didn't experience the crash any more with 2.8.15