Are you Bonding the Sub to your Playbar?

Also, the Sub will only Bond (connect) to a stand-alone speaker, soundbar, stereo pair or Amp as a singularity. Each of the aforementioned devices are called rooms/zones. The Sub cannot Bond (connect) to multiple room/zones. *

Make sure you have not disabled the 5Ghz (WiFi) option for the Playbar.

* The sub will not Bond (connect) to a Roam, Move, Port or the discontinued Connect.

It sounds like your Sonos Sub is having trouble maintaining its connection with the Playbar, even though it works fine with other Sonos speakers. Try these steps:

1. Reboot Everything – Unplug your Playbar, Sub, and router for about a minute, then power them back on.
2. Check Wi-Fi Interference – Ensure your Sub is within range of the Playbar and not facing interference from other wireless devices.
3. Re-Pair the Sub – In the Sonos app, go to Settings > System > Your Playbar] > Remove Sub and then add it again.
4. Use Wired Connection – If possible, try an Ethernet cable to see if the issue is Wi-Fi-related.
5. Update Firmware – Make sure all your Sonos devices are running the latest software.

If the problem persists, Sonos Support may need to help diagnose a deeper connectivity issue.

Moderator edit: This post is likely AI generated.

Is your Playbar connected via Ethernet?  Is WiFi turned off for the Playbar?