It works fine for me.
Assuming that you are using a Comcast supplied gateway device, try disabling the Xfi Advanced Security feature as a work-around for now and see. It's buggy ! And there is currently no way for an end-user to be able to whitelist anything;
To disable the Advanced Security feature in xFi, select the Account icon from the top-left corner of the Overview tab on the xFi app and then select xFi Advanced Security. From here, select Disable under xFi Advanced Security and follow the on-screen prompts.