Fair warning, lots of detail. I’m a software engineer with familiarity with networking architectures so I’ll be direct. I've recently upgraded both my router and modem, which is where issues began.

Single floor apartment that’s less than 500sq feet. Three Sonos:One devices, none more than 3M and a single wall (wood framing + sheetrock) from the router, signal strengths are extremely high (-30dbm) and there’s no more than 4 of my neighbor’s networks competing on any channel (1/6/11). A few neighbors use the in between networks but they aren’t meaningfully contributing to any added signal load on 1/6/11. iPhone XS with Sonos S2 12.2.3

System was originally hooked up with ‘Modem 1’ and an older Linksys 2.4 single band router. Sonos was stable, with Alexa enabled, no issues.

I updated to a dual-band ASUS RT-AX86U. I reused the old SSID and password so I didn’t have to login the 9 devices on the network again, and had no issues. Sonos and Alexa both worked great.

I then later updated to a new modem with an uprated bandwidth. This is where the issues started. Sonos devices were all connected to the network (per ASUS’s router interface) with high signal strength. Alexa stopped working, so I began to troubleshoot. NOTE: I was NOT able to resolve this issue, and cannot tell if it’s a firmware issue on the devices, or an application bug.

First step: One by one, factory reset the Sonos:One (hold link button on the back through power cycle until status light flashes orange, then set up in the app). All setups went fine, but the devices would drop out of the app randomly, coming up sometime later. Through all of this, I could see the devices were connected to the router via router dashboard. I was unable to get a consistent ping from my desktop to the devices - sometime one packet would be returned, sometimes none. I was unable to get music successfully playing, and unable to run Trueplay, apparently due to a poor connection.

Second step: Unplug all devices. Reset router both in software and via power cycle. Reconnect devices and factory reset one at a time. Same result as above - instability of connection and unable to play music / Trueplay.

Third step: Move router to fix on channel 6. This got a connection to all devices, which decayed over time. I was, however, able to get music playing. I attempted to run Trueplay, but that failed. I also failed multiple attempts at Alexa setup (following all proper troubleshooting there of removing the skill and devices, reconnecting, etc).

I was about 4 hours into this headache and said F it and just hardwired one node in. That’s inconvenient, it puts it in a poor location and looks awful. However, I was then able to run Trueplay, install Alex, etc. I assume that the devices automatically flip over to their mesh network when one is hardwired.

I’m leaving this here for two reasons:

1. To see if anyone in the community, or any Sonos engineers, can comment on this incredible network instability on an incredibly powerful network. As mentioned, the bands aren’t exactly cluttered with 4 networks per band, and the signal strength of -30dbm is incredible. Also - this issue only seemed to begin when my modem was updated from one running at 250Mbps to 450Mbps, which doesn’t make any sense to me.
2. For further documentation of troubleshooting or tips in case others run into this. I’m worn out from working on this for 4 hours so leaving it for now.