Rekordbox DJ - Output from DDJ800 stops, when typing in finder

I run RB on a MBP 2012 with SSD and 16GB Ram and a DDJ 800 without any problems during the last 3 years.

One week ago, the following has occured:
Rekordbox is playing and when i swich from Rekordbox to the finder and type in somemething, after some keystrokes, controller output stops.
It only occurs, when i type in something in the finder, not eg in a browser.

The only thing which helps is to restart the DDJ800, to disconnect it or to press in RB the button "PC Master Out". Then the outputs start playing again.

The problem doesn't occur with my other macbooks. Only with this one.

So i have deleted the whole macbook and set it up and have installed the latest version of RB and the latest sounddriver.

But ... the problem ist still the same.

Is there anything else i can do? Now i'm completly lost :-(

Thank you for your support,

Oliver