Follow the directions in the link. Also the switch needs to connected to the main node (router) and not a satellite node.
https://support.sonos.com/en-us/article/recommended-settings-for-using-sonos-with-ethernet-networks

@AjTrek1 thank you very much for the help. 

i tried the guidelines but still connection lost to the playbase. Waited for 10mins still nothing.

Then I tried unplugging the power for the playbase & sub, connecting the ethernet to the playbase, then plugging in the power to playbase & sub simultaneously. 

Finally it worked!! All speakers are now WM:0

Oh my this was getting so annoying I thought I needed a new managed switch with STP smh

Thanks again @AjTrek1 

@Iki Zamri 

Great news! More times than not the tried and true reboot resolves a multitude of issues.

Since a simultaneous reboot fixed things I’m wondering if it could be an underlying network issue.

Many folks have had hard to diagnose grief from their Sonos at updates, reboots or power failures that were solved by adding static/reserved IP addresses to the router’d DHCP settings.

Only takes a few minutes to do and doesn’t hurt anything even if it isn’t the solution.

@Stanley_4 Now that you mentioned it,  I actually did fiddled around with my router abit before the simultaneous reboot.

I resolved the issue by:

1) Set my router for address reservation for Sonos speakers,

2) Change VLAN ID for guest network to 592,

3) Unplug playbase, sub & ethernet,

4) Plug in ethernet on playbase,

5) Plug in power for playbase & sub simultaneously.

Boom. All 3 speakers are now in SonosNet. Checked the system WM and got all WM:0

I’m not sure whether steps 1) & 2) were necessary but at least it worked.

Before SonosNet activated, i couldn’t see the Sub’s Wifi connection or IP address on my router. I could only see the playbase’s & One’s Wifi connection. I believe this is due to sub was bound to playbase as ‘sub’.

The 1x One was not bound to playbase.

Playbase WM:1

Sub WM:2

1x One WM:1

After plugging in ethernet on playbase(only) and SonosNet activated, I can see all 3 of the speakers’ connection on my router and the status is ‘ethernet’
 

Playbase WM:0

Sub WM:0

1x One WM:0

I was expecting to only see the playbase’s connection on my router as ‘ethernet’ but I guess SonosNet is telling the router otherwise.

Not complaining tho, just sharing.