My Deco M5 units will no longer successfully do Ethernet backhaul on a switched network. The firmware on my switches has not changed for 6 years, and all of my hardware is the same, and at some point the TP Link units just decided to stop back hauling unless they are connecting physically togeher with an Ethernet cable. The second any managed or unmanaged switch is used, backhaul fails to work. They are all in AP mode, and this is running behind a fortinet fortigate 60D. This has been so frustrating and I am just about ready to pick up a differnt platform because, to me, this is unacceptable. My last ditch effort is to reach out for help here.

I have tried dell switches, tp link switches, dlink switches, fortinet switches, and Netgear switches. Any switch I could find, I tried. Same issue. 
 

Ideas?b