Probably nothing.  Wait until Sonos either provide a roll-back or fix the mess they've created. 

Sigh. Now all I can do is listen to the one station my system is set on at the moment by physically turning it on at the speaker. This is a disgrace. Wish I’d known before I upgraded but I assumed it was a necessary upgrade. Thanks for confirming my frustration, anyway! 

You are in good company - there are probably 1000s of unhappy bunnies out there

Got through to Sonos help. Workaround is to unplug my Bridge. Apparently this will be fixed in a few weeks but in the meantime at least I can use the app. 

Sorry, I meant BOOST (not Bridge).  

Buy a new wireless speaker system? SONOS obviously hates their customers.

I tried getting some technical support to solve some problems and the wait time was more than 2 hours and no chat availability…..  Good luck!  If possible see if you can downgrade your app if you are on Android.  That might allow you to restore the basic functions you need.

Updates are created to improve the function of the app.  Everything has gone backwards. The lag, switching songs after 5 seconds after play, the loss of my timer at night is my biggest complaint. I listen to music all day and set the timer before bed. Now I listen to my iPhone at bedtime. I have been using Sonos since the early 2000”s and this has been uncharacteristically disappointing. Who was responsible for such an amateur app design? Why would you ever release an app with so many flaws? For a sound system that started out as state of the art- I can’t understand how this was acceptable in their minds.