I think its time to send the Mamba Max back tho cc.

[Dagger Thrasher]

Sounds like a dodgy solder joint to me, so I'd check all your motor lead joints as well as the battery plug like you said. It's worth checking the motor itself too.

Don't send it back to CC until you've exhausted every possibility though. It'd be really annoying if all it turned out to be was a solder joint or something that could be fixed in 5 mins.