@Adex1 

Deco P9 can use powerline backhaul, but it will switch to WiFi backhaul if it can't use powerline. Even if it uses powerline, if Satellite P9 is not on the same circuit breaker as Main Deco, speeds could be low. So, it is hard to tell what is happening with your Deco 3, without additional info from you.

Open Deco 3 info page in Deco app and see what it reports there, example:

In that example, Satellite Deco Office uses WiFi for backhaul. Share screenshot of what you see for Deco 3 and I may be able to give you suggestions on how to improve WiFi on it.

  @Alexandre. 

Thank you for your input!

I went into the app to check what you have suggested, and I noticed that it switched (without no input from me) from the first picture, to the second. Does PLC means that is not using WiFi?

  @Adex1 

PLC means P9 connects through powerline. If PLC symbol appears and dissapears, that means P9 can not estable reliable connection through powerline. P9 switches between powerline and WiFi. That would explain slow WiFi speeds and timeouts for devices connected to Deco 3.

Deco P9 uses same powerline technology as standard powerline adapters. You can google for what could interfere with powerline adapters, and see if you have that and if you could remove that. For example, dimmable lights and anything that has motor (such as fridge) could interfere with powerline adapters performance.

You can also try to find better place for Deco 3 and these would be my suggestions:

1. Just power off Deco 3 and see if remaining two Deco could provide reasonably good WiFi coverage for your office;

2. Try plugging P9 to every electric outlet in the office, maybe there is one that will be better;

3. Bring Deco 3 to the room left of the office, on the same floor, try every electric outlet there;

4. Take Deco 3 downstairs to the ground floor and try with every electric outlet in the room under the office room.

See which place gets best possible WiFi coverage for the office and leave Deco 3 there.