If Comcast wants to change your IPv6 prefix there is nothing you can do to stop them. It wouldn't surprise me if they change your prefix now and then just to make it hard for you to run a server. Maybe they can sell you a business class account with a static prefix assignment?
Yeah I'm hoping it's not nefarious. :)
Issue is getting the speed/bandwidth on the business accounts. A 100MB line on Business isn't cheap…
Or, if this enhancement gets applied to PFSense then it may resolve my issue.
https://redmine.pfsense.org/issues/3029