Have you tried turning it off and on again…?

What does the LED look like when you power cycle the Sub?

Edited as replied to wrong person.

Reboot the device the Sub is bonded to. The last firmware update gave me this problem with all bonded devices.

Thanks.  LED is solid white.  The app keeps saying the sub is connected again but it never shows up on the device list in settings

Had to pay someone nearly $500 to come over to fix my system.  Each device on the network needs to be factory reset and reinstalled for the new app to work properly.  This is a cluster and Sonos should be ashamed of releasing a half baked product.   Good luck to all.