DFR0548 freezes micro:bit v2

I am experimenting with a DFR0548 on a micro:bit v2 and a micro:bit v1. The program controls 2 motors of a small car model. The current is provided by a large battery bank (5V 3A). The car is controlled by a program written in Makecode.

With the micro:bit v1 the programme works without problems, with the micro:bit v2 and v2.2x the controller freezes after a very short time.  

Does anyone know this problem? What could it be?

Many thanks