Your post title and the information you provide are confusing. Are you trying to setup a Play 5 (gen1) on an S2 network? If so that can’t be done as the Play 5 (gen1) is only S1 compatible.

Have you tried setting up the device by temporarily wiring it to your router?

No a play 5 gen 1. On a gen 1 bridge and or boost. I have another play 5 and it connects fine but my second speaker says it can’t connect to the network. Which is the temporary Sonos network 

If it’s just one of two that is failing, it’s possible that there is a failure in the electronics. I assume you’ve factory reset the ailing device? If so, I’d connect it with the Ethernet cable so it shows up, and submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it. Don’t post the resulting diagnostic number here, they get sensitive about GDPR.

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 Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.