@Hovercraft it's showing a drop of 50% of the speed of Verizon. I am 1 floor above and has the deco setting in middle of all rooms. Max speed I saw today was 310. Verizon speed are slow today compared to 900 down - 900 up average to only 450 down -750 up overall I am very happy. Thank you so much again.

The speedtest has no influence on the up and download if QoS is not enabled, at least that is what I observe, and that makes sense I think.

Still getting 30mbit/s on my iPhone, 250-300mbit/s on my MacBook pro and iPad Pro all on wifi, same location inside my house, and 950mbit/s on a Linux computer wired to the main Deco. Apart from iPhone performance, that is ok with me without I'm being impressed about it. 

There must be something wrong with the iPhone (setup) I suppose.

Mads

@Rubberduck May be you are right but after making that change. I am getting 340 down - 540 up speed across the home. Better than my 100 mb :) may be restarting the verizon router and deco main unit may also help.

thanks!
Parag

@Socalbruin 

I had the exact same issue. Set-up the first Deco M9 Plus and tested the speed via the Deco app and it was showing 200+ Mbps speed physically next to the unit. It was a mistake not to test using other apps/Spectrum speed test website which I later realized. Once I set-up the second unit on upper level and tested the speeds less than 10 feet from it, the Deco App kept showing speeds upwards of 250 Mbps but the other apps were showing speeds in the range of 30-70 Mbps.

Once I disconnected the second unit, the speeds across the apps was similar an in 200+ Mbps range.

I have the latest firware on both units. 1.3.0 Build 20190821 Rel. 54023.

Looking forward to a response from Tp-link on it. If you have resolved the issue somehow, please let me know the details.

@Hovercraft thanks mate, your solution worked for me.👌

@Hovercraft Thank you so much! It worked! I was very disappointed in my Deco M4 until I followed your comment. TP-Link Team should find a way to fix this problem as soon as possible. Although this problem is simple to fix, 90% of people will not know about QoS. Even I have used a lot of devices from TP-Link and I cannot know this.

Updated:

- If you have QoS issues like other people, you can switch to "Access Point Mode" so QoS will be completely disabled. Your network speed will be back to normal,  the weak point is that you need an additional Router.

- If you still want to use "Router Mode" you must set QoS to maximum and "Set high priority" for the device you want to optimize Internet speed. But this can only help you reach 90% of the power of the Internet only. Because of this problem, Firmware still has an error.

- If you do not want to set anything, but if you have already missed the QoS set, you should set the Internet speed of the package you are using directly.

Note: It seems that the Firmware of TP-Link has tested the Port Ethernet that you plugged in and measured its speed. If you plug a Port from 100Mbps into Deco 1Gbps it will interpret as QoS for 100Mbps, while 1Gbps then QoS is 1Gbps and it will also automatically Throttle if you do not have "Set High Priority". The more devices, the worse QoS will become.

@Krolled murderer!

@paraglohiya 

Referring to your comment regarding 800-900 on FiOS internet, and only @ 90 Mbps anywhere via wireless.

I am also on a Gigabit FiOS connection, and have had this same issue for months, and finally started troubleshooting more in depth. I had a eureka moment today, which simply by going into the "Antivirus" settings on the Main Deco Router and turning off the "Malicious Content Filter" . My speeds immediately increased to 250-350 Mbps. This was connected to the main unit. I haven't checked my satellite units yet.

I will continue to monitor the speeds on my side, but i'm somewhat surprised that the "Malware content Filter" which, in their words sound like a simple blacklist, shoudln't cause any slowdown:

"Blocks malicious websites that are listed in the Trend Micro database to ensure you can surf the net in safety"

I'd like to hear from TP link on why such a performance hit is happening with that setting.

@Hovercraft Thank you!!!!  I was on the phone with Tp Link support for two hours and they had no answer!! 

Thank god i found your post.