Sounds like you might possibly have a dirty pin connection. Many recommend cleaning both surfaces with alcohol. I like carb cleaner myself, but you have to be careful because carb cleaner will melt some plastics. So never spray it directly on any plastic surface. Spray it on a Q-Tip and then quickly clean the mating surfaces.
I find a HUGE help is a good macro photo of both surfaces. A good macro photo will reveal issues one could never see with one's eyes.
Another thing you might try is to air out the brushless motors. Sounds like you might have some debris in one of the motors.