Nighthawk RAX45 IPv6 routing works then stops. Resumes routing after RAX45 reboot, then stops again.

Nighthawk RAX45 Firmware Version V1.0.4.100_2.0.64.   Advanced settings IPv6 on LAN as "DHCP" or "Auto Config" the IPv6 routing to the Internet STOPS/FAILS with either config.  WAN side is DHCP with Comcast and IPv6 address is present.

Same results with these clients, Linux Mint 20.2, Android 11, Windows 10 And Windows 11. Wired or Wireless connections, for clients that have both.  Note: Android used here only gets IPv6 address by "Auto Config" on RAX45.

Immediately after a RAX45 reboot, all client OS's noted above, their IPv6 connections complete to "ESTABLISHED" (not verified in Android), Then go the TIME_WAIT as expected. After some time all new IPv6 connections show only "SYN_SENT" with no completion to Established. I will try to track the exact time to failure.  I know for sure now it is under 24 hours.

Once IPv6 connections fail, a Windows OS client with a ipconfig release/renew of DHCP address, or a client reboot of any OS, or a client network disable/enble, each of those show client IPv6 address is present on return to link up, but still no IPv6 routing completes to Internet sites. IPv6 specific nslookup or dig for Internet sites also fails with no response. After RAX45 reboot those nslookup/dig do return results as expected.

On LAN side IPv6 address is present, and the client link local fe80:: is present.  The route table shows the RAX45 "router interface" link local fe80:: address as the default route for IPv6 for the Internet at ::/0 as expected.  This is also true when RAX45 is routing successfully.

I have repeated the RAX45 reboot process 4 times over the last few days and that solves the no-IPv6-routing, but only for a short period of time.

Looks to me like this Nighthawk RAX45 has a IPv6 routing process failure. Did the process crash?  Anyone seen the same?

NOTE:  IPv4 is not affected.  All client devices are dual stacked, getting both their IPv6 and IPv4 addresses from the RAX45, so all Internet sites connect via the IPv4 addresses when IPv6 connection attempts fail to complete.