@CrisisWolf 

On my Deco M9 Plus, with smartphone wirelessly connected to it, and with gigabit Internet I can have up to 650Mbps with wired Main Deco and up to 430Mbps with wireless Satellite Deco.

I hardly ever see less than 250-300Mbps in my speed tests with Deco M9 Plus.

When you do Test Internet Speed from Deco app, what is the result? This will test wired connection between Main Deco and Truespeed router. If they negotiated 100Mbps over their Ethernet link, that might be the problem.

See this document: https://www.tp-link.com/us/support/faq/1601/

It is possible you would just need to increase QoS value to 600Mbps down and 600Mbps up, to unlock the speed.

If that does not work, there is another option. You have Truespeed WiFi router, you said, would you consider running Deco mesh in Access Point mode? If yes, this is how I run it and I can share with you all other settings from my Deco mesh, perhaps replicating them would solve whatever issue there is.

  @Alexandre. Thanks for your input.

This is the result of the built in Deco test and a PC on ethernet gets similar results.

My phone on the TrueSpeed WiFi when next to it (but has poor range) is

Whereas on the Deco WiFi

Not normally as bad as that mind but still no higher than 80mbps ever.

I read about the QoS and have changed from Auto to Manual and will see what this does.

What is Access Point Mode? I have heard of it but that is all.

  @CrisisWolf 

In Access Point mode Deco mesh provides WiFi coverage, Truespeed router will manage network: IP address allocation, static IP addresses management, content filtering, etc. Deco will pass through WiFi traffic without applying any bandwidth throttling and content filtering to it. 

In that mode, Deco provides maximum WiFi speed and performance it can deliver.

AP mode is useful when you want to find if any Deco configuration setting impacts WiFi speeds of your devices. In AP mode, all these settings will be disabled.

Also, in AP mode, because network will rely on Truespeed router for everything, every device connected anywhere is a part of same network. I have wired shared printer/scanner connected to my ISP router Ethernet port, I can use it from any device on my home network without issues. Same for file server.

Finally, in AP mode there are much less restrictions on how you could wire Satellite Decos with Ethernet, if you have that ability.

You can easily switch between Access Point mode and Router mode. If you miss important features disabled in AP mode, after troubleshooting you can just change Deco mesh back to Router mode.

See these FAQ documents for more info:

What’s the difference between Access Point mode and Router mode on the Deco?

How to set up Deco to work in Access Point mode

General questions about Ethernet Backhaul feature on your Deco

Hi @CrisisWolf,

I have a similar experience with Deco XE75 Pro with Samsung Galaxy A32 5G and I just recently posted it in this forum
https://community.tp-link.com/en/home/forum/topic/546618?replyId=1152524

My other 20+ devices is working fine and picking up good WiFi (300 - 500 Mbps), while the A32 5G from 5 feet, only get's 30 Mpbs. From 30 feet away, the signal gets weak and speed is around 0-30 Mbps.