A new standby mode is introduced in firmware 537.
zZ is signalled on your product in SoundSpaces if your product is currently in standby mode.
To wake your speaker from standby mode - simply tap your product in SoundSpaces.
Libratone App is not mandatory to wake your speaker from standby mode. You can also wake your speaker from standby mode by tapping the Nightingale on your speaker. Your choice.
Read more about standby mode in general here.