Likely your WiFi is on the edge of working or not and the extra traffic generated by the PLAY:3’s pushes over the edge. You may notice that the problem is worse when the Café is full of people because humans absorb some WiFi energy.

The fastest workaround, if practical, would be to wire one or both of the PLAY:3’s to your network.

First, I suggest that you submit a Diagnostic immediately after one of these events, record the confirmation number and contact SONOS support. Network issues leave tracks in the diagnostic.

If we had more information about your network configuration we could offer more focused help.

I did wonder if that was the case.

the router is an ISP provided Technicolour one. I simply have all my devices in the building connected to it by Wi-Fi, no more than 10-15 devices at a time. One sonos is only 3m away from the router, but the cable route would be a messy one. The 2nd is on the floor above, so no chance of cabling that one.

Try the cable to see if it solves the problem. If it does, buy a Boost to wire to your router and let the Play3 go wireless again 

You only need to wire one device to take all the Sonos devices off WiFi and onto SonosNet. 

How does the system work if you play only the nearby speaker? Do you Group the speakers in order to play the same music in both areas? If so, note that the first speaker in a Group becomes the “Coordinator” of the Group. All network traffic for both speakers will go through this unit. If that 2nd floor unit is struggling with it’s wireless connection, making it the Coordinator is counter productive. Make sure that the nearby speaker is the Coordinator.