Hello again,
So after a lot of adventures with the odrive it failed quite spectacular with a lot of smoke.
The odrive was switched of when it happened. Only the ground was connected to the battery.
The motor may have spinned a lot
What could have caused it?
Oofffh, that really got burnt out
Yowch, nasty. 
When you spin a motor connected to ODrive, the motor naturally generates an AC voltage proportional to its speed, and this will drive a current through the body diodes of the FETs, which act like a bridge rectifier and will charge up the capacitors. If, for some reason it draws a lot of current through this bridge rectifier, then it will cause the FETs to heat up, producing about 2W per amp as heat due to the 0.7V silicon diode voltage drop across each of the FETs when back-driven like this.
Also, the ODrive will turn on (you will see the green light come on) and it will potentially start running its startup actions. If the startup actions include motor or encoder calibration, you could be in trouble if it tried to do that with a fast-spinning motor. It would energise the coils at a random timing with respect to the spinning motor, which could produce a higher voltage than the motor’s EMF at that speed.
What was the mechanical situation that led to this? A runaway winch? A vehicle rolling downhill?
Is it possible that the motor spun significantly (more than 20%) faster than would normally be its maximum speed if you set a continuous torque demand at 56V input?
If so, then the voltage generated by the motor could be higher than the capacitors, FETs and gate drivers on the board can handle.
BTW: Does M1 still work? 
Well, after a co-worker took a good look at the robot he figured out what possibly went wrong.
There was a short in an other motor close by and those cables touched the frame. The power that the motor generated with driving the robot went through the steer motor and then through the odrive causing it to fail.
The motor connected to the odrive didn’t move from footage we suprisingly had.
Still that the odrive failed is weird.
Maybe, but the magic smoke genie that escaped did cause some damage and we do not trust the board. The genie did leave his smell behind that still is noticable, even after 24 hours with a night outside.
Possibly, if the frame went “live” then the current path could have been through the FET bridge rectifier of the unpowered ODrive, and from there to ground.
What voltage do your drive motors run from?
As a general rule, your frame should be connected to -ve battery terminal anyway, ideally with a nice short low-impedance copper braid directly to the battery lug. That way, any shorts to the frame should blow the appropriate fuse, and the grounded frame should protect against noise/EMC issues.
