Hello, I think I'm at the same frustrated point as the OP before he found a solution, I haven't. I have two former T-Mobile AC1900 turned RT-AC68U, I have hard reset both, upgraded to latest firmware, I have tried adding the node wired, wireless, I have tried all wired laptop to router to node, no success, I have tried laptop wireless, router to node wired, no success.
Tried laptop wireless, router wireless, node wireless, no success. Tried hard reset node and then adding node wired and wireless and no success.
Tried hard reset for both, started router from scratch and added new hard reset node and nothing.
Both my 2.4 & 5 SSID have the same name but I don't think that is the issue. Any other ideas?