The first thing I’d try is a refresh of your Sonos network, by unplugging all Sonos devices from power, then rebooting your router. Once the router comes back up, plug back in the Sonos devices. Forcing a reboot of both the software on the router and the Sonos might help.

However, if you’re still having trouble bonding the Sub to the pair of Fives, I would recommend that you submit a system diagnostic, 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.