A customer which has a M210 RTK reported a strange crash and send the drone to maintenance. He said that he heared a strange sound and the drone fell down, braking many parts.
Ok, I got the equipment and the first thing the came to my attention was a burned motor (LFRONT motor). I have seen many kinds of crashs and fly aways, but I have never seen a burned motor in the matrice series.

So my question was: did it burn during flight or something else went wrong and it got stucked on the ground? I don't see any of them happening, but...

I opened the motor/ESC and I found that the red wire was also burned and it was loose on the ESC side (picture 1 and 2 attached). So, if it happened during flight, of course that the drone would fell down.
Analyzing the flight log, I confirmed that the M210 lost the LFRONT motor during flight.
Log: https://drive.google.com/open?id=1jhU9LTlkzD-Fu_xxVuSl0skVmz2hV6Vz

A strange behaviour came to my attention: LFRONT motor current started to oscilate few minutes before the crash (picture 3). According to the log, LFRONT motor current was around 50A and oscillating. The other motors were fine.

I couldn't find any log event reporting a motor/ESC issue before it touched the ground.

So I ask your help. What could cause this current oscillation? Did it burn in the air? Why? Have you seen something like that? Did I miss anything important in the flight log?

Thank you.

Obviusly is a warranty case for DJI, this wire burn out and caused the fall down

Please ASAP send M210 to your  dealer a ask about open new case for you dron

Yes Leofuica, I agree with you.

Hi RLProto, sorry for the late response, the drone must be sent to DJI official repair center for further diagnosis, our facility will help to figure out what happened and verify whether the warranty service can be provided. If you need any further assistance during this progress, please let us know.

Obviously an ESC or motor failure.  Maybe the solder wasn't too great on the redwire and the manufacturer ran out of solder to properly finish the job.  The connection wasn't too good and drove the amps way up due to impedence.  It's like trying to put lots of amps in a thin wire, eventually it will melt.  Perhaps something in ESC failed and couldn't regulate the voltage properly driving way too many amps to the motor to handle.  What else could it really be?

Could you tell me which tool to check the motor current?

Was this within the warranty period and did DJI cover the repair expense?
I had the Flight Controller Board (main control board) die while just out of warranty and they sent a $3,000 USD repair bill.
Oddly enough they don't tell you that they had to break the M210 RTK apart to fix it (water sealed?) and charge you for all parts involved.