原来是Apple Store发行证书存在问题.

It turned out to be a problem with Apple Store Distribution Certificate.

我遵循了此步骤并且在重新创建分发证书后，所有问题都得到了解决，因此不需要将我的Xamarin.iOS版本升级到9.6.1.9.

I followed this steps and after recreating the Distribution Certificate, all problem was sorted out, so didn't need to upgrade my Xamarin.iOS version to 9.6.1.9.

希望这可能对其他人有帮助.

Hope this might be helpful for other people.