Sonos Arc repeatedly drops off network, taking entire surround group with it — firmware 18.4

As you believe the Arc is at fault and not your network. I suggest you run a diagnostic and make note of the Reference ID (do not post it in the community). Call Sonos support as they have tools to analyze the data. Hopefully it is a network issue and not a failing network interface card (NIC). Best of luck!

EDIT:

To your question...We in the community cannot verify that what you are experiencing is a “known issue” of any sort.  We are not technical support.

I don't pay much attention to versions, app or firmware, just always updating to the latest releases. That would be my suggestion to you as a first try at a solution as getting help with old versions is difficult. 

The Sub and surrounds hunting around with the loss of the Arc isn't something to worry about as they are trying to deal with the loss of their primary network connection, the 5 gHz Sonosnet generated by the Arc.

Have you observed the Arc when it drops off? Any change in the solid white status light? 

Have you confirmed the power cord is fully seated in the Arc socket, often folks don't push hard enough to get it fully seated. A light touch of DRY silicone lube on ONLY the outside of the cords molded end can help reduce the needed force. Wet or greasy lube will make a mess, don't do that!

As you have reserved addresses already that isn't the issue but it may be something else network related or a glitch in the Arc, a diagnostic sent and a call to Sonos may reveal something.

I avoid complicated networking so I am little help there.

There are a couple good posts here about Ubiquity best practices that you could check  to see if your settings match.

Could also be potential wifi interference , particularly from outside the network. Hard to tell, without access to the hard data we’re not exposed to, when you submit that diagnostic. 

Hardwire the Arc by Ethernet, and remove the static IP addresses on the surround and sub. They aren’t needed as they get their signal directly from the Arc, not your router.
 

If you can’t hardwire the Arc, then try just removing the static IP addresses from the surrounds and sub anyway. That could be causing your Arc issues.

To add to this, make sure you leave WIFI enabled in the Arc’s settings. While some say it can be turned off, I have left it enabled on my Arc with zero issues.

Yes - good point. WiFi must not be turned off on the Arc, or the surrounds and sub won’t be able to receive the dedicated 5ghz signal from the Arc. 

Could be another VLAN bug, try not using it on a VLAN. Also use the Uni logs to see if something happens right before it drops eg frequency change, ip addr change, switching to a different AP etc.

Very unlikely the DHCP reserved (static) addresses are an issue. They aren't needed on most systems, are needed on some, and some folks just like neatly arranged IPs and assigning device names.

I have (actually have to have) assigned DHCP reserved addresses to all my Sonos, to include multiple Subs and two sets of Surrounds with no issues.

I did have issues with my Arc and Sub gen 2 both wired, support suggested not wiring Subs and Surrounds which cleared that set of issues for me.

I am currently all Wi-Fi but once the "disable Sonosnet" option becomes available I will be connecting Ethernet to several of my Sonos. Not really needed but the cables are already run so it is just plugging them in.