When you force an IP address change for your Comcast connection, two things may happen.
Your new IP address may be in a different subnet than it was before, and that can change the routing path in both directions.
Any particular IP address that Comcast assigns to your connection may actually be a "new" IP address in an IP address block that Comcast recently purchased. Some web servers (and/or web hosting services) do indeed block specific IP addresses and address ranges for a variety of reasons. The operators of those sites may not be aware that the ownership of the IP address block in question has changed, so they simply continue to block access from that IP address range.
Unless you can/will supply specific information, nobody can do anything but reply to your post with generic guesses.--
We can never have enough of nature.
We need to witness our own limits transgressed, and some life pasturing freely where we never wander.