I was having the same issue as many have mentioned here, 200mbps from the ISP but on 20mbps from the Deco wireless.

I'm not sure what fixed it for me to be honest, but I changed the QoS to 1000/100, removed priority devices, updated the Deco to latest firmware (and I suspect this was the fix) rebooted them all as part of the update.

I also changed my ISP router (Virgin Media) to Modem Mode - I'm now getting 215mbps on speedtest- faster than the ISP router 

Good luck everyone, this sort of thing is infuriating 

  @MJC_OK I am getting 930mb wired into the M4 Deco main (PC tested), 930mb wired out of the Deco main (PC tested). WiFi next to the Main 337MB.

Reading all the posts (and trying every fix) and potential solutions, this product is not capable of working to spec out of the box.

I'm going to move to a supplier with a product which works.

I bought it two years ago but it's a big avoid for future proofing.... just will not work to spec.

Can't see why I would buy another product from these guys.

Si

  @SuperSi 

I have the same issue.  Wired great, Wireless not so great.  They don't seem have tried to come up with a solution in the couple of years since this post was created.  

EDIT IN: I'm leaving my post as is, just in case anyone else has a similar issue, but I just restarted the Deco (it wouldn't actually reboot from the app, regardless of what it said, so it was a hard reboot, i.e. I pulled the plug) and everything seems back to normal. I cannot believe I didn't try turning it off and on again before writing on here... So the oldest solution in IT appears to have worked again.

I'm yet another person with issues with the speed from the M4, specifically over ethernet. Until recently everything worked fine. I was getting expected speeds over ethernet. 

However, today I noticed that speeds have dropped significantly. I am not aware of anything changing. all cables are the same as when it all worked fine, which I believe was literally only a day or two ago. The decos underwent a software update recently, but I'm sure I recall it all being fine since then.

I have my decos in access point mode, the main deco connected to my modem/router via ethernet, and then my pc is connected to a gigabit tp-link switch which is connected to the other ethernet port of the deco. 

I have a raspberry pi NAS connected directly to my Sky modem/router. Using iperf3 today between the Pi and my PC, I was getting max throughput of 95Mbits/second. Transferring files to the NAS I was getting a max transfer rate of about 11.3MB/s. Previously I was getting 75-90MB/s. My PCs internet download speed via a speedtest is about 92Mbps down and 14.1Mbps up. I should be getting 150/30. 

So in the last day or two, something has happened that's reducing the ethernet speed that travels through the Deco. 

WiFi is fine, it is only the ethernet port speed that is an issue. 

Going to my network connections panel and double clicking my ethernet connection gives a connection speed of 1.0Gbps.

My Raspberry Pi which is connected directly to the router/modem got 148/31 on a speedtest, so it is getting expected speeds, it is only traffic going through the Deco that has the issue.

I cannot change QoS, as the Decos are in access point mode, not router mode, so the QoS feature is not available. I can't see anything in the app that is relevant to change. 

Anyone got any ideas? Like I've said, it was all working fine yesterday or the day before, so it is a very recent issue.  

Further to the above, where restarting the Deco solved the issue, it would appear the issue has reappeared.

My throughput is again not going above 95Mbps.

This makes it seem like the ethernet ports on the Deco are changing from Gigabit mode to  Fast Ethernet (100Mbps) mode and I have no idea why. 

Any ideas from anyone would be appreciated.

Dealing with the same issue. Deco M4 connected to a Virgin Superhub 3 set to modem mode. Wired connection from Deco reaches ~550 Mbps, but a smartphone connected to the WiFi (and positioned right next to the main unit) only shows 250-280 Mbps. I have tried:

• Updating both Decos to the most recent firmware
• Setting QoS to 1000/100 and removing all the devices from priority mode
• Swapping two Decos around
• Resetting all the devices on the network
• Using both the top and the bottom port on the main Deco to connect to the modem

…but nothing changes the speed over WiFi. Will most likely return the product if this does not improve.

 Bought 3 Deco M4 for our house. Plan is 400mbps but phone connected on the wifi just getting 50mbps. So frustrating and waste of time and money.