(Pfsense with LACP WAN) Can't obtain IPv6 address

Just so we’re clear, I’m not bonding two internet connections. This is one of those “multi-gig” cable modems, the Arris SB8200 in my case. Instead of providing one 2.5, 5, or 10gbase-T port, they put two 1gbe ports on the back to achieve the “multi-gig” speeds. After enabling LACP on the modem, I created a LAGG interface that’s assigned as the WAN connection. After several reboots I can only get an IPv4 address from the modem, while Pfsense reports IPv6 as unknown or pending. The network card I’m using for my WAN interface is a Intel 82580 I340-T4 E1G44HT, with the first two ports configured as the LACP-WAN interface.

Here are some screenshots, starting with the problem at hand:
Dashboard

I’m having this exact same issue now as well. Did you ever get it resolved?