Xfinity wifi not connecting to certain apps

Recently, when connected to my home wifi network (Xfinity gateway and router), my Android device will not connect to the Xfinity app (it just shows the cycling dots). It also will not push-sync emails to my email client or load certain apps (e.g., Weather Underground). All other web-browser traffic seems normal. The issue goes away if I connect to a VPN while on my home wifi network or if I set up a DMZ using IP 10.0.0.2. Any ideas what could be causing this behavior and how to fix? @Xfinity Support