@David-TP 

The Deco's are set to run in access point mode.

I have been able to further isolate the problem. Both ethernet ports running from the main deco to the satellites appear run fine at 1000Mbps. However, one ethernet on each of the satellites seems to be limited to 100Mbps (one out of the two). When testing with speedtest running on my iPad connected to either of the "limited" ports on both of the satellites, I get the limited 90-100Mbps speeds. Numerous resets of the devices connected to those ports & resetting of the satellites doesn't seem to have resolved things.

The other ethernet port on each satellite seems to be fine and providing 1000Mbps to the devices connected.

  @David-TP

I've been running speed tests at various times of the day for the past few days + checking the stats on the devices connected to those ports. They remain at 100m/s.

The bottom port (2.5G/s) remains unaffected on both satellites & is used to backhaul to the main deco. On one of the satellites it is the middle port and on the other satellite it is the top port. At first I wondered if it was a cable degredation problem or the devices but when connecting an iPad with a 1000M/s Ethernet Connector & Cat 5e cable to both of the problem ports, I still only pull 90-100M/S when the problem free ports remain close to my broadband speed of 900M/s+.

Hope this helps!

  @tomglazed I have exactly the same set up and i'm having the same problem so you're not alone....

  @David-TP 

Just adding a +1 to this.

I am having the same experience across the satellites and on both gigabit ports on the main deco. Issue here is of course the 2.5port on the main deco is the fibre in, so no now the outbound backhaul is capped at 100

Is it possible to get an update on this issue please mate?

@David-TP 

Do you see any chance of TP Link looking into this? Certainly seems that a few users are experiencing the problem.

  @David-TP 

Much appreciated, I can confirm receipt of the email and look forward to working to find a solution.

For further context in recent developments to try and identify a solution, I recently look at my main modem/router (BT Smart Hub 2) to see if settings within that could be impacting the Deco’s. One setting that seems to have changed the problem is in UPnP: the smart hubs have a setting called “Extend UPnP Security” on top of enabling UPnP. I disabled “Extend UPnP Security” but ensured UPnP is kept on. This seems to have changed the impacted 1Gb satellite ports behaviour to instead of capping always at 100mb but to stop working all together (no IP get’s assigned to devices connected to those ports); other ports still work flawlessly. Obviously this isn’t a desired outcome, I've since rewired by network setup to use the one fully functioning port on each satellite to then wire everything off of. Hopefully it gave any clues as to what could be a root cause, something to do with UPnP could be it?

I've sent the above in response to the initial email in the event it helps give any further context/root cause places to start off with.