After trying all types of fixes and being on the line with Comcast for 2 hours they fixed it finally. When in Bridge mode the Ethernet cable plugged into the Main Deco MUST be plugged into LAN Port 2 (Top right on back of XB7). Reason being is there is a setting you need to check when you log into the XB7 router.
Go to Hardware --> LAN --> Under Port 2 (top right in image below) check the box next to Associate Ethernet Port 2 to XFINITY Home Network. Now my Deco works perfectly with my modem in Bridge mode!