@Sunshine 

Thanks for the reply.  I had been doing that, but speed tests are so spotty that sometimes I would get 400mbps, other times 700mbps, and all over the board.  I finally got a speed test server to give me 2,000mbps, so it seems like it is working, but it's such basic information I don't know why "Strong" couldn't be replaced with the actual connection speed while using Ethernet.  Hopefully that can be a feature request.

Oh, and it would also be nice for wired devices to be able to show their connection speed in the connected client list right below the ethernet icon.  Either a 10g, 2.5g, 1g, 100mb right below the connection.  There are no other indicators, so something in the app would be nice.

  @NikkoToska 

> My rental apartment has wires in the wall which I'm using as an Ethernet backhaul to the second unit downstairs.

This is the most likely problem. Depending on the age of the apartment or cabling retrofit, as well as building plan and therefor cable length, the signal quality may not be high enough for 10GbE traffic. What happens in that case, depends: devices could negotiate lower speed, like 1GbE or 2.5GBASE-T or 5GBASE-T, but that's no guaranteed; another possibility is higher error rate, with retransmissions which may look like latency spikes to the end user; yet another, although rarer, is the connection going up and down. I'm not sure what Deco does in the latter case, perhaps switches to wireless backhaul and back to wired?

Perhaps someone from tp-link can advise on how to interpret status lights and status in the app to exclude the possibility of older cabling giving you grief.

The other option is to get someone with a cable tester to visit your place and check the cabling.