Have you tried unplugging the One from power for a couple of minutes and rebooting your router? Are you able to wire any of your Sonos speakers (not a Sub or surround speaker) directly to your router with an ethernet cable?

The first thing I’d try is checking for a potential duplicate IP address. Since, on most routers, that’s a difficult thing to do, I’d just unplug that Sonos One from the power supply, then reboot the router. Only when the router comes back up would I plug back in that Sonos One. 

If it continues after that to have an issue, I would recommend that you submit a system diagnostic as soon as you’ve noticed it has dropped off and call Sonos Support to discuss it. It might be worth doing a second one after the Sonos One has rejoined the network, so that they can do a “compare and contrast” investigation. 

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.