Hello, thank you for the replies.
Regarding IPv6, the devices on the LAN are showing an IPv6 prefix length of /64, as shown in the Terminal output from one of the devices. LuCI has not yet been used to verify the specific IPv6 prefix that Flint 2 is handing out on the LAN side.
The IPv6 prefix delegation being provided by Comcast to the Flint 2 on the WAN side is currently unknown. From information found on the Xfinity forums, residential connections have been reported as receiving either a /60 or /64 DHCPv6 prefix delegation. Since the WAN-side delegation has not yet been verified directly, I don't want to assume which prefix Comcast is providing in this case.
There is also a concern regarding the data-corruption bug affecting forwarded TCP traffic above roughly 200 Mbps with GRO enabled, as described in this thread:
The Internet connection is 1 Gbps download and 125 Mbps upload, so the reported GRO issue could be relevant to this connection. Apologies for not including the connection speed in the earlier replies.
Thank you for your help.