[ALL] 6in4 Tunnel Not working through XB6

I've got all the details posted over on the Shaw Community, but thought I would cross-post here to get a few more eyes on it: https://support.shaw.ca/t5/internet-discussions/xb6-blocking-6in4-ipv6-tunnel/m-p/32143 But the breakdown essentially is: XB6 (CGM4140) seems to not be letting 6in4 (protocol 41) traffic back in. Worked fine on a Hitron CGNM-2250, but not on the CGM4140. Comcast users on a similar sounding platform also reporting this issue: https://forums.businesshelp.comcast.com/t5/Connectivity/IPv6-over-IPv4-6in4-seems-to-be-blocked/td-p/41807. This also sounds somewhat similar to a "VPN blocking" issue with the XB6 from last year: https://www.dslreports.com/forum/r32733051-Shaw-blocking-VPN where it sounds like there were also some stealth firewall rules still in play even in bridge mode that were eventually corrected in a firmware update. Anyway, if anyone else has seen this specific issue, a post over at the Shaw community would be appreciated.