I had both motors hooked up to Two separate escs off of one battery I had one BEC connected to my receiver ch3 and the other bec I had removed the ground wire and just had the signal wire plugged into an auxiliary channel and slaved it to channel 3 mixing. One of the motors & esc I used before together, but the other set was bran new. I didn’t think about putting the screws too far in on my soda can motor mounts. It’s probably what did it.
The only thing that I ask is what did you have connected to the 30 Amp speed control? It it were nothing then you have bought a bad 30 Amp speed control. It is obvious that the speed control output was so to speak over loaded or "shorted out". Double check you wiring polarity just to be sure your wiring was correct. Read most of the above and see what happened, "KISS" is something that one has to learn and its not easy.