@David-TP 

Hi, can I have the model number of your new TV?

Prism+ Q55-QE (Google TV) 

Here are some suggestions for your reference:

1. Disable "Beamforming" under Deco App>More>Advanced. 

2. Set "Connection Preference" for the new TV to 5GHz of the satellite BE85.

Will try the above suggestions now and update again.
Thank you David!

  @David-TP 

1. Disable "Beamforming" under Deco App>More>Advanced.

 - Beamforming has been disabled

2. Set "Connection Preference" for the new TV to 5GHz of the satellite BE85

- new TV set to 5GHz of satellite BE85

Unfortunately, the losing of wifi connection is still happening, it reconnects after a short while though. just keeps getting the notification that wifi connection is lost.

The same thing is happening to my PC too - connected via wifi.

I have to force wifi connection by turning on and off wifi on PC to get connected.

PC is set to 5GHz of satellite BE85.

This is getting worrying.

Thank you.

  @ByTP 

Disabling beamforming and assigning a particular Deco and frequency, as described here, helped fix most my issues, but I also had to set channel widths to their lowest values... 20mhz for 2.4ghz, 80mhz for 5 and 6ghz. I have over a 100 devices connected to my Deco network, including many cameras and 2 PC, one doing video conferencing. I think I needed to chose "slower" settings in order to stop ongoing interruptions from happening.

I chose to have a main and 3 satellite units to achieve a strong signal all around my house, but I have probably created some instability by these many Decos... 2 top of the range Decos would probably have been ideal.

  @BPCS 

Thank you for your suggestions.

I will lower channel width for each band and try again to see if there's any improvement.
I have only about 10 devices max connected at any one time.

Main and 1 satellite deco BE85 to cover 1500 sqft.

Main alone cannot provide good speed to the furthest room therefore using MOCA 2.5 to connect to satellite at furthest room.

  @ByTP 

I would think 2 BE85 and only a few clients, would work well... but maybe you are in a very crowded wifi environment... narrowest channels plus a reboot and then running Deco network optimisation, will be good to see how that works.

  @Kyne 

I find this confusing too.

The BE85 I bought in Taiwan is the (US) V2 version.
Can it also use the (EU) V1 version 1.2.1 firmware?
Are the V1 and V2 firmwares interchangeable?

And why doesn't the official website update the latest firmware?!
I see the V2 firmware is stuck at 1.0.1.4 and hasn't been updated since.
Why?
Is the latest BE85 firmware 1.2.1 or 1.3.0?

Is there a 1.3.0?

Should there be a separate discussion thread for the 1.2.1 firmware?
Otherwise, no one will know. There's a 1.2.1 update with bug fixes.

This performance really doesn't justify the price.

  @Diplofu 

Perhaps the removal of the top plastic cover on the routers can allow them to ventilate better. 
 

Also, if possible, use the second lowest 10G port instead of the one at the most bottom may help with heat issue. Unless you need to use 2 x 10G ports, otherwise just use the one which is the second lowest. 
 

As for losing connections frequently, from the advice of fellow forumers, I no longer set the 5GHz channel width to 240mHz, I'm using 160mHz. More stable now. 
 

Beamforming on or off not a major issue now. 
 

Now hoping to the combined ethernet and wireless backhaul feature to be reinstated into the new firmware. It's been removed ever since 1.2.0. Real pity as it managed to pushed the wifi speed a lot. 
 

Hope above helps.