By the off chance have you set both connections as static IPs, and the same IP?
The LAN IP addresses are set up manually and are static, distinct and addressed in a range below where my router hands out dynamic IP addresses.
Main router being an ASUS N16 running DD-WRT v24-sp2 (06/08/12) mega firmware which should be irrelevant AFAIK.
For example miners are set 192.168.1.99 then 192.168.1.98 and so on down.
The DHCP server handles the wifi addresses which come in at 192.168.1.100 and up. DD-WRT is pretty good with allowing the use of static IP addresses in conjunction with the DHCP server as long as the addresses are outside of the range the DHCP server is instructed to use which is the case. I can see the dynamic wifi IP addresses it issued through my router GUI and everything appears fine in that regard. Bitmain uses Paragon Technologies for their network adapters all having a MAC Address of 20:59:A0:B2:xx:xx (xx being variable to address the specific device) so they are easily identifiable on the network.