@realjax 

Hi, Did you choose the wrong modem?

Since I checked under your TP-Link ID, it is a 3-pack Deco M9 Plus?

As for your current issue, could you please help me confirm the following details:

1. How often would the speed drop to 20 m/s, even 0m/s from 300m/s?

2.When it started, How did you temporarily restore the speed, like restarting the Deco?

3. Did both Ethernet connection and wireless connection have the same issue？

And since you mentioned that “I have other access points that easily reach 200mbit”

The other access points, I think it is not Deco and could you please help me draw a picture of your network topology?

Thank you very much.

@TP-Link 

Yes, sorry I have the m9 plus. 

1) continuously.

2) resetting didn't help. Unplugging all three from the mains did after a while restore speed.

3) Cisco router -> m9's as access points and also the router is an Access point and I have an apple time capsule thingie working as an additional access point. Also the DHCP server is running on Linux.

@realjax 

Heres the current speed of the Deco m9 (using phone @2.4 GHz) which is in clear view , non obstructions.

And here's the speed (phone @ 2.4 GHz) using my routers acces point which is equally far away but BEHIND a wall..

Both tested several times, this is the average speed...

@realjax 

Hi,

Is your network topology, like:( the full line is Ethernet connection; dotted link is the wireless connection.)

Since the 2.4ghz speed is highly affected by the wireless condition, how about the 5ghz and Ethernet speed from Deco? Did they behave the same?

And if only leaving the main Deco M9 Plus connected to the Cisco router, would the speed get a little bit better?

Did Cisco router, Deco, and Apple capsule use the same SSID for their wireless network?

Thank you very much.