Bluetooth has a delay for most codecs. Do not ask me how it is exactly done but there is a feedback to the application so that it delays audio to match video for the bluetooth delay. Some years ago a new Linux audio subsystem was developed, and this thing did not work at start but they fixed it later. From that time is my memory.

Unmounting does not mean the device gets invisible. You could still mount it again by e.g. clicking it. Still it is unmounted and safe to be removed. Disconnecting the device from the system makes it disappear but that is not required for unplugging/ejecting.