@brooklyn27 

I think you are overcomplicating things. Some of TP Link FAQ articles are not very clear, but even then I am not sure how you deducted from one you referred to that you'll need separate VLANs to run Deco in AP mode with Ethernet backhaul.

Deco mesh running in AP mode is the easiest setup: you can connect Deco nodes with Ethernet cable anywhere in your network, and that includes Main Deco. No specific LAN/VLAN setup is required.

This is what I have, with Deco mesh in AP mode, and it works on my network:

router - Satelline Deco M5

          - switch1 <-Ethernet-> switch2 <-Ethernet->  Main Deco M9 <-WiFi-> Satellite Deco M9

>"If i wifi mesh or use direct cable between decos it seems to be ok."

With troubleshooting you've done, it points at issues with your switches or wiring between switches. Including possibility of some type of conflict between Deco firmware and specific switches/wiring you have.

@Alexandre. Thanks for the confirmation that you have successfully managed this setup.

I was going to try a vlan as an alternative to separate ethernet that i tried that worked. 

However what i have discovered is that i did have a dlink router further up in the network and can only assume this has the dlink switch issue.

I have removed it and seen much better performance.

There are still some issues with repeated dns requests and acknowledges that seem to come in bursts from time to time but all in all a much more stable network.

thanks for the response..