I got the same message from the Linn support, with additional info that Linn devices don’t send these IGMP join messages while in sleep, which does explain my case of endpoint disappearing over the night while in sleep. More on that later.
AFAIK Roon is using multicast and mDNS (IGMP) for endpoint discovery only.
See more here:
This post states that IGMP is not needed, however that it can affect the multicast traffic that is needed for discovery process. It also states that Roon is not using multicast for streaming but unicast direct to endpoint streaming. The mDNS is only used for endpoint discovery.
However, my understanding of mDSN is that it is actually using IP Multicast Groups, specifically this one:
224.0.0.251: mDNS for Device Discovery (also known as Bonjour)
For the IP multicast groups to function properly, we need the IGMP functioning properly on our switches/routers. Or we need to disable IGMP all together not to interfere. When IGMP is off, multicast messages should be flooded to all ethernet ports by the switch/router, which would give us no problems.
In my case, I need IGMP enabled on my router to control IPTV multicast streams, so I don’t have an option to disable it. Actually, I’m not even sure if IGMP is a problem in my situation, or we have a problem with mDNS.
On that note, Linn support says that the device is sending IGMP join messages, but that Roon has problems with cached entries. That would mean that Roon has a cache of endpoint devices (names and IP addresses) which it collected via mDNS discovery process. I’m not sure on the lifetime of these cached entries, but we can only presume that there’s a conflict with old and new entries when my Linn device boots up from sleep and starts sending join messages.
I would then absolutely recommend pinning an IP address for Linn device on your DHCP server (router). Weird thing happened on my last Linn firmware update, even though I had a static IP address for my Selekt in the DHCP, my Selekt DSM got a new IP address when updated with new firmware. I cannot be 100% sure that the new firmware made that, but it was very strange. Do double check your static IP assignments even if you’ve set them up before.
Also, I would recommend updating/shutdown of your Roon server and then shutdown of your network chain including any routers and switches. To hopefully clean IGMP group memberships and Roon mDNS cache.
From my last hard shutdown of the entire network chain and Selekt endpoint, I did not have any cases of Selekt endpoint disappearing. That was 3 days ago, fingers crossed it stays that way. 