I use WebEx at work. I could use it at home until a month ago. After talking to WebEx and my work IT's department, it looks like the problem is somehow comcast at my home. I tried logging into WebEx at home with a personal hotspot, and it worked. I used wifi at a friend's house (who uses Comcast) and it worked. I've tried logging in at home using wifi but also directly connected, and neither works. I get messages like "We hit a glitch connecting to the Webex server. Please try again later" and "This site can't be reached. Please check the proxy and firewall." I don't have firewall active, and IT looked at proxies on my laptop. So what's going on at my home with Comcast?
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;