WRT1900ACS router sending IGMP to unknown/unset netmask

I've got a Lenovo G50 running 14.2 that is giving me grief. Traceroutes to sites I'm visiting shows latency in the ~20ms range, yet page loading is s-l-o-wwww. Concurrent Wireshark sessions show many RST from akamai, many TCP retransmissions, and a number of TLS errors where the length of the TCP segments are too long. And when checking UDP conversations I see that the router is sending out membership queries to 239.255.255.250 when the netmask set for the wireless network is 255.255.255.0 Clues, tips, questions, redirects to other fora or sources welcome. This may or may not be the place for this question, but I look to slackers for quality commentary.