@MacDaddy215 Glad I could be of service.  Seems that with each update the issues are not resolved.  Be sure to check this setting every so often as it defaults back on every update for me.  Let me know if there is anything else I can help with!  Namaste!

I bought M9 Plus (3 package) at Costco last weekend, and having the issue.  I have been reading all comments, but have not find a solution for me yet.  

I tried Hovercraft way, but still does not solve the problem.

Deco app show 500+ Mbps, but but speed test on mobil/laptop via WIFI always show less than 100 Mbps.

Wifi connection to ISP router/modem show much faster speed ~250 Mbps

Connect by ethernet cable to main box also show <100 Mbps

I tested connections around 5ft to main box.  Unplug slave box does not show any difference.

If I cannot resolve this issue soon.  I will have to return it to Costco.

@Khoa I was in exactly the same situation, about to pack up the system and return to Costco.  I decided to try one last thing: I deleted the network and restarted the entire process.  Unplugged the modem, and the two satellites.  Plugged the modem back in, and the main deco (the router) was flashing blue.  I set it up and speeds right next to the router were at max levels (which I wasn't even seeing before).  I turned on IPv6 and fast roaming (had not done this my first time).  I then proceeded to plug the two satellites back in.  They flashed red, so I had to reset them.  But after that, they proceeded to connect and I am not basically getting 90% of max speed throughout my entire house.  BTW, I used third party speed tests during the entire setup.  I believe the speed test in the app tests the speed of the router, not your phone or device.  I'm not a technical person so no idea why this worked for me but perhaps worth a shot for others in the same boat - thanks!

Hi, Thanks for the tip @RBNY , i have the same issue and I will try your suggestion. However, could you please be more specific about deleting the network. What did you do to delete it? Thanks!

@RBNY.  Thank you.  I will try your suggestion tomorrow.  Really hope it works.  Thanks

For what it's worth, I did a lot of testing trying to increase my speeds to expected levels. Here's what I found. 
 

My provider modem has a speed test and of course it shows great throughout, exceeding the 1Gbps speeds I pay for. 

Performing a speed test from the deco attached directly to the providers modem I see speeds of around 700-800Mbps up/down. 

Directly connecting a new Mac book to the providers router shows speeds in line with the deco speeds. On wifi the throughout is less, as to be expected. 
 

My desktop was the biggest issue showing really slow speeds in the 100-300Mbps range. 
 

I did find that the speed test websites where all consistent. I then read an article on HTML overhead slowing the speed results. As such I downloaded apps for testing which showed the higher throughout rates. 
 

I do no get full 1Gbps to any device, but at 80% I'm happy. Given the hardware all have different configs this is to be expected. 
 

My point, set the QoS throughout to max 1024 up/down. This will get you maximum throughput. Reboot the deco devices when you make this change as well. 
 

I do have both QoS and anti virus enables. I did find best results enabling custom settings on QoS with full priority on all configurable items. 

@jubilantjesse 

Same problem here. Paying for Comcast 300mbs. Speed Testing my laptop which is two feet from my base deco. And have it hard wired from deco base directly into my laptop.I get a speed of 30mbs. I got this Deco Mesh, because of this speed issue that I had with Google Mesh. Not a bit of difference.

@bobdeco check your cables. I found an cat6 cable in my network which was causing the connected device to have bandwidth limitations. I recently replaced all my cables end to end. 
 

Also, under the deco QoS setting in the app set the bandwidth up/down to the max, 1024. My testing shows I see 80% of this number on all devices. This should be higher than your connection and be good for you. I'm still convinced QoS and this setting have something to do with the issue... 

Select custom under QoS and set everything to high. I also added my devices to high priority. 

@TWPS I was having same problem in Los Angeles area with my download speed with Spectrum. I have the minimum speed package which is 200mbps and during peak hours starting at 5 PM, I could hardly get over 30 mbps and at times, it went down to 7-8 mbps. Needless to say, very frustrating as you can't stream anything without buffering constantly. I had tried everything that has been suggested on this forum with no luck including resetting the modem every 30 minutes, which is annoying and even with that the speed would drop in about 10 minutes. The last thing I tried was take the modem back to the Spectrum store and swap it out with another modem and Voila!! the problem solved. Now, I get 220-230 mbps constantly even during peak hours with wired as well as wifi applications. So, in my case, it wasn't the Deco M9 but the Cable company Modem that was apparently defective and would not hold speed and I am really glad that I stuck with the M9s and didn't return them in frustration as I really like the simplicity in setup, operation and efficiency of the Deco instead of returning them and buying something else. Just thought I would share my experience in case anyone is having this problem with the cable modems and would like to try this out. Good luck and happy surfing and streaming!!

TWPS wrote

@bobdeco check your cables. I found an cat6 cable in my network which was causing the connected device to have bandwidth limitations. I recently replaced all my cables end to end. 
 

Also, under the deco QoS setting in the app set the bandwidth up/down to the max, 1024. My testing shows I see 80% of this number on all devices. This should be higher than your connection and be good for you. I'm still convinced QoS and this setting have something to do with the issue... 

 

Select custom under QoS and set everything to high. I also added my devices to high priority.