Not really enough information to tell, but I’d be betting on some wifi interference , possibly coming from outside your network. There’s conflicting statements, pointing to impossible situations, though, I’d probably submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your Sonos system and network.

I Agree with @Airgetlam. Although he mentioned WiFi interference he is correct regarding conflicting statement in that your system is hardwired per your description. 

Also, unless you are confusing your speakers being hardwired to the Amps that’s not the same as having the Amps wired back to your router (creating the SonosNet) via Ethernet cable which is what the community refers to as hardwired.

One more question… is there a Sonos Bridge component in your setup? If so the Bridge could be the issue as it is outdated and known to cause problems in some setups. If so remove it and see if the drops continue.

So your choices are to follow the advice given by @Airgetlam and/or explain/clarify a few things regarding your Sonos setup.

The speakers are wired to the amps. They are not WiFi. Yes, there is a bridge. I’ll disconnect it to see if that helps. Thanks. 

At least one of your CONNECT:AMP’s should be wired to the network after you power down BRIDGE.

Ethernet to one or both Sonos is the way to go.

If you really miss the Bridge you can find the (going away) Boost in the Sonos Store “Last Chance” section. I wouldn’t get one unless I had no other option but hanging wire the spouse would not approve of across a room.