What does "blocked" mean exactly? What happens when you try to browse one of those sites? Any error messages?

All dynamic IPs like the ones Comcast provides to residential customers are, or should be, on blacklists like the Spamhaus PBL in an effort to make life harder for spammers and others engaging in Internet abuse. See https://www.spamhaus.org/pbl/.

All of those messages come from the destination systems, not from Comcast's cable internet service. You'll need to contact the site Admins or webhosts to find out what they are objecting to.

For "my.xfinity.com": if an employee doesn't reply to your message here, Comcast Security Assurance should be able to help. You can reach them at 1-888-565-4329 (from https://internetsecurity.xfinity.com/help/report-abuse/). Note that this is NOT one of the general customer service numbers. The first-line reps there are sometimes not very helpful, so you may need to be persistent and keep at them until you get a satisfactory answer.

Thanks. I will try this route. I have opened a ticket with netgear also.  I can't even reach Xfinity's site. You would think they should have a clue with that happening.