Best answer by Airgetlam
Is your router set to automatically change the channel it is broadcasting on? It could be that it is switching to a channel that it thinks is "better" and the PLAYBAR is having trouble chasing the signal as it changes.
The other suggestion that *may* help is to assign reserved IP addresses to your Sonos (shoot, do all) devices that are connected to your wifi. This will require some effort on your part, reading the instruction manual for your router. Look for something about reserving IP addresses in the DHCP table. This will help your router keep a single IP address for all of your devices.
Finally, there's always the possibility that the wifi card is going bad in your PLAYBAR, since the surrounds and SUB connect to it for signals, and not your local wifi signal. So, if it happens again, connect the PLAYBAR to your router with the ethernet cable, and then submit a system diagnostic, and contact Sonos to discuss it. There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.