I am having issues running 2 APs in one location. Both on same floor - but through many walls. Both AP as direct POE wired. One SSID network. Here is setup:

SG2210 main switch

SG2008 secondary switch connected to SG2210

EAP670 - main AP in hallway. Standalone works great.

EAP655-Wall. Second AP located 3 rooms away connected to SG2008 switch. When enabled, things go bad.

My main network with just the 670 running works great, though some devices have weak 2.4 wifi signals. Added EAP655 wall pointing away from other AP. Hoping to cover those weak signals. First had them on different channels for 2.4 and 5. Then used the AI (which also puts on diff channels.) So, I know the channels are not overlapping. Disabled fast roaming as well as that might have been causing issue for some more finicky devices. 

Initial setup works from. Some devices slowly moved over to new AP. All good. Eventually things start dropping off the network. All on 2.4ghz. Thermostats, Hue lights. Things like that. Just complete drop. If I remove the 655 and reboot 670 switch, things will reconnect slowly and come back.

No mesh setup. And followed all guides. What am I missing? Would really like to use the second AP to get better signals on other end of area.