The otherwise() rule is only invoked when no other route matches. What you really want is to intercept the $stateChangeError event, which is what gets fired when something goes wrong in a state transition (for example, a resolve failing). You can read more about that in the state change event docs.
The simplest implementation for what you’re trying to do would be something like this:
$rootScope.$on('$stateChangeError', function(event) {
$state.go('404');
});
Also, since $http itself is built on promises (which resolve resolves), your ConcernService method can be simplified down to a one-liner (I realize you expanded it for debugging purposes, but you could have just as easily chained it, just FYI):
var ConcernService = {
get: function (items_url, objId) {
return $http.get(api_url + items_url + objId);
}
}