Originally shared by Sebastian Szafran
Bad luck, I could smell the X axis driver chip.
Stepper motor power level set to 0.35, cooling fan on but it burnt-out 
Set to 0.35 how?
What Vmot are your running?
Does not seem that you were putting s lot of stress on motors - just probing and holding ??
Unless you have done a lot of custom wiring and pinout reassignment on Due to G shield interface, $pl=0.35 does not do anything. Power level is set via DtoA converter on DUE that gets connected to Vref on driver circuits on tinyGV9 and other G2 prototypes.
I don’t believe that is implemented on standard GShield.
@sszafran more likely is the heatsink. We stopped shipping them as they tended to move during jobs and could actually ground out on stuff. Just like that. Not saying this is it for sure. But its where I would put my money. 
@Riley_Porter_ril3y Should I stop using heatsinks and just the fan for cooling or make sure heatsinks are mounted in a way they cannot move (with a help of some thermal paste)?