CLLocationManagerDelegate's (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error not called when in App is in BG

Question

My locationManager is setup to work in BG (allowsBackgroundLocationUpdates + in capability Background Modes: location updates is checked).

My CLLocationManagerDelegate's

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray<CLLocation *> *)locations

works fine when application is in BG.

But,

- (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error  

Does not get called when in the application is in BG. When the application is returned to FG then the method is called.

• I checked this on iOS 10.

Any ideas?