Any chances (not certain here) that either your switches or router are using RSTP rather than STP? While I’m no expert in that, there have been previous reports of network storms caused by managed switches, but I don’t know how quickly that occurs. One key thing tends to be people are better off with unmanaged switches, which apparently handle the issue automatically, whereas managed switches don’t. 

You may want to post one of your submitted diagnostics number here, on the offhand chance a forum moderator, who has access, can see something that a phone rep missed. 

I’m using A Verizon FIOS CR1000A Gateway and both managed and unmanaged switches. if you dig around you’ll discover a number of “fires” burning around that router. Just this week I caught it assigning duplicate IP addresses for two SONOS units -- even though these addresses were reserved for other (non SONOS) units.  Also this week I noticed some IP addresses that didn’t make any sense. I fixed the duplicates with freshly reserved addresses for the two SONOS units, backed up the router settings, and factory reset the unit. This cleared all of the strange IP addresses. In the past, I’ve made a practice of rebooting this Gateway monthly. Since I reserve IP addresses, the reboot does not usually cause any trauma. Yesterday there was a power failure and the network came up without a fuss.

Thanks, Airgetlam. I’m uncertain whether either my switches or the Verizon CR1000A router use RSTP or STP and I’m pretty sure my switches are unmanaged (I’ve certainly never managed any settings for them -- everything just plugs in and works fine). This is also the same exact setup I had before with Xfinity.

My most recent case number from Sonos support (not the actual diagnostic number) is ********.

Anyone have any thoughts/recommendations on the best 3rd party support options? I have neither the tech know-how, the time, nor the patience to figure this out further myself. Have given it the ol’ college try.

Moderator edit: removed case number

Well, that’s a good sign. Unmanaged switches are easier to deal with, but shoots down my thought process. 

i wouldn’t post a support case here (GDPR and all) although i would post a diagnostic number. I’d recommend editing your post, if you can, otherwise someone might call in and pretend to be you, and mess things up for you. 

I wouldn’t / can’t recommend third party options for support. Too many differing needs of a mix of Sonos expertise, and networking expertise. Especially places like Best Buy Geek Squad. You could get lucky, and get someone who ‘gets’ it, but much more likely to get a minimum salary person who means well, but doesn’t understand how the system works. 

There are several users here in this community who have significantly more networking knowledge than I, @buzz is one of them, and has already responded here.

I’d still post those diagnostic numbers you submitted, it’s possible one of the forum moderators will be able to see something that may not have been noticed by a CSR, as I said before. 

@Dubblebees.

 If you have only two AMP’s in your system and assuming that they are within wireless range of each other, wire only one of them to your network and allow a couple minutes for the AMP’s to reconfigure after you remove the network cable. STP and RSTP become a potential issue only when multiple SONOS units are wired to the network.

@buzz @Airgetlam 

Gentlemen, thank you for your follow-up on this. I tried buzz’s suggestion last night of wiring only one of the AMPs and unfortunately got the same sequence of events … the system came right back up but then I lost it overnight.

I didn’t keep track of any of the earlier diagnostic codes but re-ran the diagnostics this morning. That # is 1377032361 in case any of the forum moderators are able to look into it further.

I appreciate everyone’s help!