RMerlin, It looks like all of the ports are listed upside down. Tested on AC3100 running the 380.57 alpha3 build:
WAN in the firmware Sysinfo page = LAN 4 physical port.
LAN 1 firmware = LAN 3 physical.
LAN 2 firmware = LAN 2 physical.
LAN 3 firmware = LAN 1 physical.
LAN 4 firmware = WAN port physical.
WAN in the firmware Sysinfo page = LAN 4 physical port.
LAN 1 firmware = LAN 3 physical.
LAN 2 firmware = LAN 2 physical.
LAN 3 firmware = LAN 1 physical.
LAN 4 firmware = WAN port physical.