never get block called in iOS8.4 on iPhone6

[BeingX]

i use it like this,but the status block never called.

• (instancetype)init
  {
  if (self = [super init]) {
  _reachability = [Reachability reachabilityWithHostName:DEFAULT_SITE];
  __weak typeof(self) weakSelf = self;
  _reachability.reachableBlock = ^(Reachability*reach)
  {
  weakSelf.sNetWorkStatus = [reach currentReachabilityStatus];
  };

    _reachability.unreachableBlock = ^(Reachability*reach)
    {
        weakSelf.sNetWorkStatus = [reach currentReachabilityStatus];
        NSLog(@"UNREACHABLE!");
    };
    [_reachability startNotifier];
  

  }
  return self;
  }

[BeingX]

when restart system ，it normal again,it confuses me