Been having this problem off and on for a few years. I tried all of the usual fixes like turning off and on Wi-Fi, turning off and on mobile data, checking all network connections, reinstalling the Xfinity Connect Mobile app to no avail. I recently discovered that if I sign out of the Xfinity Connect Mobile app, and then sign back in, my email functionality is restored after it re syncs with the server. I hope that helps somebody out there.