You're being quite clear - no worries. But it is very puzzling. I'm really curious to find out what's going on. You might be right about your low voltage under load guess. Maybe just try adding more cells to your pack? You'd still have voltage drop, but my understanding is running an ESC too far under voltage can be hard on it too. And you have plenty of headroom voltage-wise with the motor, no? I'd also think about adding a capacitor bank just to smooth out those spikes. They can cause failure too.