There are many reasons as to why your Xfinity internet is slow all of a sudden. The causes include home network challenges and ISP connection challenges. The main reasons for a slow internet connection are internet congestion during peak hours, damaged cables, poorly performing router/ modem, poor positioning of the router, interference by home devices, and over-utilization of your internet. Others may include a slow internet plan from your ISP. You can explore the various ways to get the best out of your Xfinity internet here.