Likely, there is a local network issue. If you describe your system and network we can make some suggestions. You should also submit a diagnostic and post the confirmation number here. SONOS staff can analyze the diagnostic.

I certainly agree with buzz. In the meantime, it may not hurt to do a simple network refresh, by unplugging all Sonos devices from power. While they are unplugged, reboot your router. When the router comes back up, plug back in the Sonos devices.

Then you can submit a system diagnostic within 10 minutes of experiencing this ‘loosing (sic) of speakers’, and call Sonos Support to discuss it, or post the diagnostic number here for a Community Moderator to pick up.

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, there are more options available beyond just the diagnostic analysis.

As an explanation to the comments from @buzz  and @Airgetlam, please see this post that explains a typical cause for this.