Mine too, today. What have you done with our systems Sonos?

Had the same issue, I tried everything - factory reset of all 3 speakers,reboot my wireless network.. tried so many times and even when i succedded and the speaker was found i got the message that it wont be visible.. and it wasnt. nightmare. 

so - i found a solution here in the community - i deleted the new app, downgraded to old version - downloaded the old version from apkmirror.com

first of all - i switched off the option of automatic upgrade of all apps in playstore in android, so when i download the old version the sysytem doesnt just automatically upgrade it. 

i logged in and all my speakers were found and are functioning normal.