Not getting an IPv6 address anymore.

Sometime early 2022 something happened to IPv6 on my Xfinity Gigabit connection. I am not getting an IPv6 IP. The modem is a Netgear CM2000 which works great. I have tried to with two different routers. When using a Netgear Orbi router I am able to get an IPv6 address if I keep toggling IPv6 on and off several times. But the IP only stays for a few days and I am told IPv6 address "Not available" and have to go through the whole toggling and reboot procedure again. The other router is a Reyee R6 with which I am not getting an IPv6 address at all. This worked without problems until early 2022. What could the problem be? I have exhausted all configuration options on both routers and the router manufacturers tells me to contact XFinity/Comcast but I thought I would ask here first.