Matter-over-Thread device unresponsive

Matter-over-Thread device unresponsive

https://github.com/home-assistant/core/issues/91459

If a device becomes unresponsive (so the state changes to unavailable), the cause is in 99% of the cases network related, more specifically multicast DNS related. Take a look at your network, no inter vlan routing is supported (yet).

Also myself and others have confirmed that even having a multicast responder active on your network is enough to have thread go completely mad. For example on Unifi networks this option is known as "multicast DNS". Disable it, even if your thread border routers are on the same (v)lan.

Also bad implementations of IGMP snooping can cause issues. Even the Linux NetworkManager had issues handling the routing table from thread BR's, hence the patch in HAOS 10.

2 tips that helped me resolve the issue.

Disable any DNS especially on ipv6 DHCP
Select "Allow All" on Promiscuous Mode (VM Settings -> Network -> Advanced)

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