I noticed when mine was doing it that the red gyro light would go off at exactly the same time, and as the power from the battery goes through the esc first it seemed to be the reason.

I was going to upgrade it to a programmable esc the emax 40 amp anyway so i replaced it and that solved the problem straight away

With the eflite esc`s sometimes its down to bad soldered joints on the pcb or a failed mosfet transistor, i never found out as i changed the whole unit