TLDR; issue was caused by macOS's MAC address randomization for each different SSID on the same network.   The ARP cache on the macbook and MR57 and Gateway had duplicate entries. The macbook had saved a previous SSID with a randomized MAC address and new IP addresses were getting assigned to the same MAC address while the ARP cache had an old IP address for the same MAC address.   The fix? Changed the setting on the macbook to turn on MAC address randomization, delete the known networks and reboot all 3 devices.  Thank you for your feedback folks. I hope this helps someone someday, so I updated this thread for posterity.      ... View more