@TP-Link 

1. Could you please provide a rough picture about your network topology from the ISP modem, to Deco , then central switch?

I have a central switch in my basement.  I have wired runs to the basement, first and second floors that I used to connect the APs.  .

2.Are you able to get the constant ping spike on the wired devices when Deco is connected, or the ping was sometimes good, while others had a huge delay?

I had everything connected for about 2 weeks.  I moved one of the APs on the second floor to a different part of the house to try and get better coverage, but otherwise nothing else had changed over that two weeks.  Over those two weeks I slowly started noticing performance problems on the WIRED devices.  If I bypassed the switch that the APs were connected to and went directly to the ISP pings were normal, but anything connected to the central switch would have high pings and consistent packet drops.

3. And Deco X60 is working under access point mode, not wireless router, right?

Yes, the Deco is in AP mode.

4.May I know how is your internet service provider and how about the model number of your provider’s router?

My provider is Verizon and I am using the Fios Home Router G3100, which I believe to be a fairly recent model.

5.Finally, it would be highly appreciated that you could send me some screenshots about the ping spikes on the wired clients.

Unfortunately I did not capture any screenshots and I am a little apprehensive to reconnect the APs at this point.  The other thing, this did not happen immediately which confused me at first.  I initially thought I had a switch failure or a cable issues.  After replacing the switch and all cables I finally thought to remove the Deco and things snapped immediately back to normal. 

Since it took about 2 weeks before it reached a point where it was very noticable on my devices I am not sure I can capture this information quickly.

Thank you,

 -Brad