I have a Deco M5 (set of 3)

I'm connected to Australia NBN via Optus on a 50 Mbps plan

Deco #1 is connected via Access Point to my Optus Router/Modem 

My Optus Router/Modem is connected to the NBN Connection Box

My download speed is a constant 50-54 Mbps and upload 20 Mbps

Deco #2 is located on the floor above Deco #1 almost directly above.

Deco #3 is located on the same floor as Deco #2 some 20 meters from it.

The signal from Deco #3 is mainly used by the TCL smart TV

The internal walls of the home are timber and plaster 

The signal received for Deco #1 rarely exceeds 10 Mbps upload and mostly is 1 Kbps to 2 Mbps.

The signals for Deco #2 and #3 replicate those on Deco #1.

The signal received by the TCL TV is very week and I experience many dropouts, frozen screen etc.

I have run a speed check via the Deco app and it is a constant 50-54 Mbps download and 20 Mbps upload

Deco #1 is located within a meter of the Modem/Router on a desk shared with 2computer screens. The computer is on the floor, over a metre from Deco #.

The signal display on Deco #1 varies between 1 kbps to 10 Mbps but normally peaks at 2 Mbps

What do I need to do to improve my connectivity to provide greater signal strength to Deco #3 as this is the one I depend on for the TCL TV.

I'm able to operate my Wi-Fi iPad from Deco #3 most times, but still get slow performance when the signal settles between 1 Kbps and 500 Kbps.

i've also tried connecting Wi-Fi Router (Default) with a similar result.