Losing Output in the MIDDLE OF SETS!

I’m running djay 2 (on a MacBook Pro) with the Spin 2, through a powered amp. At least five times last night (in the middle of a set!), djay suddenly reverted to the Built-In Output as the Main output, killing the sound to the amplifier, and sending the output (uselessly) to the MacBook speakers. In Preferences, I would reset the Main Output and the Pre-cuing to Vestax Spin 2, and begin AGAIN. But not ten minutes later, the same reversion occurs. And after the same fix, the same problem! Again and again! WTF?!

This has happened before in rehearsals, but only sporadically. Last night had me wanting throw the Spin 2 in the garbage… Help!