Does a brushed motor need capacitor? Yes. Doesn't matter if its 2.4GHz since the back emf doesn't just generate radio interference, it can find its way into the power thus needs to be stopped at source. 3 capacitors is generally overkill, and just there to keep previous generation engineering copywriters happy. If it needs more than 1, the motor has something fundamental wrong with it.
The likeliest cause is the ESC shutting down due to an excessive current demand from the motor. This could be either the motor being naturally too thirsty, the motor being faulty, or too much prop putting too much load on the motor. An excessive demand might have caused the battery voltage to dip. This can cause some ESCs to switch off until they get the correct voltage again. Recognizing this might take the ESC some time, and might require power cycling (i.e. switch it off and back on again), OK on a buggy, not much use in a boat. You can't walk over to a boat.
The steering still works so the BEC is OK. So is the radio and the servo.