The volume suddenly drops sometimes.

Talkover might be turned on.

When it’s on, this feature automatically reduces the volume when the microphone picks up the sound from the speakers. Try to use the microphone as far away from the speakers as possible.

This issue may be caused by static electricity etc. If you don't need to use Talkover, turn it off.

To turn it on/off, open rekordbox [Preferences] > [Controller] > [Mixer].

For details, refer to the Operating Instructions > "Changing the settings" > "Changing the settings with rekordbox".

You can read the Operating Instructions [here].