Many of the better ESC's have a thermal protection circuit that will shut off the motor current if the ESC gets too hot.

Also if your running your packs too close to their limits, the LiPo cutout may kick in before you expect it to causing the same symptom.

With EDF's I find newbies tend to grossly under estimate the power requirements.

To me it sounds like the ESC either burned out or hit the termal limit.