LAGG/LACP dropping protocol 41

ISP: Comcast

Experienced this issue on a new CM1200 running firmware 3.02.01 and on a certified refurbished CM1100 running firmware 7.01.01

If I run the modem with LAGG/LACP disabled, protocol 41 (6to4) traffic passes just fine and is seen on the receiving end and returned back.  No issues encapsulting ipv6 within ipv4 traffic.  All ipv4 traffic routes as expected.

If I enable LAGG/LACP in the modem, ipv4 traffic passes fine (and is appropriately balanced across the two physical ports) however protocol 41 is dropped 100%.  The router is sending and encapsulating the traffic as confirmed by tcpdumps on the router, however the tunnel provider confirms zero ipv4 traffic received to even attempt to establish the 6to4 tunnel.  The moment I disable LAGG/LACP in the modem and tunnel re-establishes itself without issue and all is well.

Ideas?  I'm about to return the modem (again).

Thanks.