Horrible product! Doesn't always connect! You can spend 1/3 of the cost on Bluetooth products that always work! 

Have you tried unplugging the affected speaker from power for a couple of minutes and rebooting your router?

And yet hundreds of thousands seem to be having zero issues in getting their systems to work. Perhaps it is an issue local to your system?

GuitarSuperstar has started the process of attempting to resolve what issue you’re experiencing, but he might be better able to help you if you were able to provide some additional details about which Sonos speaker you’re using, and what specific Bluetooth issue you’re experiencing, as well as what device you’re trying to send a Bluetooth signal from, and frankly, any other detail you’re willing to share to help people understand the your system and the issue, and suggest resolutions for you. 

I see you own a Play:5 Gen 1. Are you sure the wifi card on this is OK? Have you tried connecting it with a cable?