system reliability

That was a poor response by the agent. I suggest that you submit again. Network issues leave tracks in the diagnostics. If there are no network issue tracks, hardware failure moves up the list of potential causes. Network issues can be intermittent. Keep a log of events. Submit within 10 minutes of an “event”.

Years ago I had a major issue in some evenings and Sunday was impossible. I slipped a copy of my log under my neighbor’s door, along with a polite note. A couple days later the log returned with annotations. Some evenings she worked out of town and Sunday afternoon she called mom. She was using a cordless phone that caused severe WiFi interference. I reconfigured my system layout to avoid her phone location and my problem vanished.

Router is connected to fiber and only used for Sonos. I only have one router.  Nothing else is connected to the router. The Sonos can be hardwired or wireless and the problem will still happen.  Works great with one speaker running. Also the distance from the router doesn't make any difference.  I only have a 750sf house 

Which model router? SONOS models? What are you using to control the SONOS system? Network switches? Other wired and wireless devices?

You say it’s not your network, but you really need to describe the network in further detail, because it definitely sounds very much like you have network issues.

You have not mentioned if you are using ‘fixed’ non-overlapping WiFi channels with a 20Mhz channel-width for example, or a SonosNet channel that is at least 5 channels away from your routers 2.4Ghz band, when wired?

How far away did you set the wired Sonos device from the router?

Plenty of questions remain unanswered here, even though you say it’s not a local network issue.

Fiber line coming into house hooked up to UniFi UDM running close to 100Mbps on upload and download 

Sorry missed a zero 1000Mbps

Most of that doesn’t make any difference. The speed of your connection to the outside world isn’t as paramount as the speed and quality of the connection between your router and your speakers. It’s pretty rare to have the error occur upstream, beyond the router

Unifi is an entirely separate thing, from my perspective. There are a lot of threads about horror stories in getting Unifi to work properly, and that’s an area I’ve stayed away from. 

@traildog,
LAN to WAN upload/download speed is not going to resolve things like SSDP (UPnP) multicast device discovery issues - There’s a common issue with default Unifi settings, especially if you have "Block LAN to WLAN Multicast broadcast” enabled and "auto-optimise network" enabled etc.

So far you’ve have not told us anything about your network that’s relevant. So I still think the network configuration is perhaps the most likely cause of your issue. You need to post the detail asked for and perhaps others here can make some worthwhile suggestions for you to maybe try.

Sorry I'm at work right now.  

Internet speed is not a critical point. When I started with SONOS I had ADSL service to the house and 100Mbps network speed. WiFi was nominally 54Mbps. Certainly, this would not serve my current needs, but I had no issues with my SONOS system.

Advertised speed is not a reliable predictor of overall performance. Recently, we changed ISP’s. The former service claimed 1000Mbps. The current service is only 500Mbps. Overall, the current service is more responsive and we have less down time.

How does the UDM connect to the fiber? What SONOS units are you using? Are any SONOS units wired to the UDM?