adding new sonos to app

Here’s an extract taken from the Staff post linked above…

In the UK, Sky Q boxes can be a challenge with Sonos, as they repeat the WiFi from a Sky router (not from other routers). If a speaker connects to one of these (common with Sonos Home Theatre products) it can result in the speaker being missing from the Sonos app. To get the speaker to show in the Sonos app, you need to disable the 2.4 GHz broadcast of WiFi from the Sky Q box(es). You can go into the Sky Q’s engineer’s menu (highlight Settings, press 0,0,1, then select Settings), go to Network and toggle 2.4 GHz wireless to OFF then click Confirm. If you do this make sure you leave the 5 GHz on so that the boxes can connect to each other. As with above (in 5 GHz section), you’ll need to split the bands to differently named WiFis in the router’s settings. If you have Sonos devices that are willing to use 5GHz (see above, under 5GHz band), you may not be able to bypass this issue without using SonosNet.

I would first move all your Sonos products to run on their in-built (wireless) connection called sonosnet - to do that simply wire one Sonos device only direct to your router. I would perhaps try wiring your Beam or the left speaker from the pair of Play:5’s - You can perhaps swap that later for one of your new standalone Sonos Ones. 

Keep the wired Sonos speaker at least one metre away from your router.

Then remove the wireless credentials from the Sonos App - see this link: 

https://support.sonos.com/s/article/3488

Try your SonosNet channel on channel 1 for the time being. See this link:

https://support.sonos.com/s/article/1219

Ensure your mobile controller device is connected to the routers 2.4Ghz WiFi network SSID and just as a temporary measure switch off the other devices you referred to as WiFi ‘Boosters’ for now.

See if that the works and that you can see your devices and are able to setup the Play:3 from factory reset (flashing green LED) then come back here and let me know if those steps worked for you.