I have a client system in development with an ER7406, SG2428P (core), SG3428, and EAP653URs. Initially, we had an SG1024 switch and ran into issues where, from time to time, most of the devices connected to it dropped off the network. We suspected this was due to Sonos (no evidence of this), so we swapped it out for the SG3428. Initially, the plan was to put all wired Sonos devices on a separate VLAN, but ran into trouble setting up mDNS. We left the system with all devices on VLAN10 with STP configured.

We have the following VLANs:

1. VLAN1 - Admin
2. VLAN10 - Home (currently hosting all devices and client Wi-Fi) 
3. VLAN20 - IoT (currently unused)
4. VLAN30 - Sonos (currently only used for a Test Wi-Fi network) 
5. VLAN40 - Guest Wi-Fi

We have the following Wi-Fi networks:

• House on VLAN10
• Test on VLAN30
• Guest on VLAN40 (also a guest Wi-Fi network)

Since our last visit, a new issue has arisen. Smartphones, PCs and other devices on the House Wi-Fi network lose internet connection - they remain connected, but have no internet. If the user joins the guest Wi-Fi network, internet is fine, so it's not service related. I have since solved the mDNS issue, so I created a new 'Test' Wi-Fi network and linked it to VLAN30. My client has been using this for the last 24h and has had no issues.

So my question is, why are devices on VLAN10 (wired and wireless) intermittently losing access to the internet? Could be a mistake with STP config? Port profiles? or something else. Can someone advise?

Thanks.