Just to let you know I finally found the real issue.
It is not obvious but I was able to narrow it down to the dock / USB-Hub I´m using.
When I connect the interface through my expensive powered Exsys USB hub (that I´m using live) the Audiobox works without any issues. I can change the settings in GP and can go down to 128 Samples without any dropouts.
But as soon as I connect it through a China Docking station with PD Charge (I bought on Amazon) it will have the strange behavior and dropouts.
When I tested another similar Docking station (also with PD charge feature which means it´s also powered) the interface wasn´t recognized at all.
So be careful with cheap docking stations.
I just ordered a USB B to USB C cable to connect the Audiobox cirectly to the Mac. I hope that will work otherwise I need to buy another Exsys Hub.