So I recently went with my SONOS move to a holiday trip 3000km away from my home wifi. At home I limited the overall loudness of all devices to 40%. Then I realized, that this limitation/setting persists even in bluetooth mode and there is no way to change this setting to get 100% of the possible volume abroad. I had to reset the whole device to make the limitation disappear.
In my option this is a bug and the volume limit should not be persist over Bluetooth and WiFi. As an alternative it may be possible to have two volume limitations. One for the bluetooth mode and one for the WiFi mode. Or the SONOS app becomes able to manage the device even when connected using bluetooth.
This problem was also discussed here.