To answer this, instead of your ISP going straight to the SE servers, the ISP connects to the VPN and then the VPN may have a different, usually faster, route to SE servers than what your ISP does for you. In this case, the ISPs have a route that aren't connecting to that particular node causing issues for Comcast users while hopping to the SE servers. This happened a few years ago as well and using Mudfish alleviated the issue for me. I'm on Centurylink now though and I'm not having the lag issue.