This is a common situation in industry where the 3-phase motor has a resistive reactance fault (as small as 1% unbalance) PRIOR to start. Insulation has been subject to excessive heating but meets IEEE std. for safe operation. The trip occurs as reverse torque is generated due to current unbalance. Overload relays protect & function as designed.
Upon resetting the "ground fault" - insulation appears in safe range. At start, current is in excess of the "norm" in the effected phase (with the reactance fault). Current exceeds the 7-25X fla (dependent on motor design) and insulation fails! I have utilized this analysis on 3-17,500hp motors with a 95-100% success rate at predicting a pending motor insulation failure!