I have used my TP Link Deco X20s (3 of them) in AP mode for a couple years.  I recently ran into an issue where one of the APs would no longer connect to the main AP.  After a lot of troubleshooting I deleted the network and factory reset all 3 APs.  Now, when I switch from Router mode to Access Point mode, 2 of the APs do not pair with the main AP (that is connected to my firewall upstream).  The main AP does pass through some IPs that are being served by the upstream DHCP server but there is no internet connectivity.  

I have deleted the network and factory reset a couple times now with the same results.  

I have a fiber ONT entering the home which then connects to my firewall/router.  That router runs to a Cisco switch uplink port and the main Deco AP is plugged into that switch.  All of my devices that are wired back into that switch get an IP and get out to the internet.

Any help is appreciated as I don't want to run a separate network for my wireless devices.