if(LF > 50){(LF - 17);} // This is because one of the wheels turns to fast for some unknown reason, it's not the driver, pwm pin, motor,..
Useless code.
Please do not put multiple statements on one line. No professional programmer does that. No professional programmer puts the } on the same line as anything else. Correcting those issues, you have:
if(LF > 50)
{
LF - 17;
} // This is because one of the wheels turns to fast for some unknown reason, it's not the driver, pwm pin, motor,..
which, I hope, makes it clearer that the code in the block is useless.
What happens if you use Motor(-120, 120) followed by Motor(0, 0) followed by Motor(120, -120) with delays in between. Perhaps the sudden change in direction of both motors causes the power surge that kills the Arduino.