Try to plug the servos as close to the battery screw connector as possible. Even if the uBEC supplies enough current, the traces might not be able to let it pass to the servos that are further away.
Are the servos now performing as desired? You could trim the header pin bottoms that are contacting the USB connector, then put a piece of electrical tape between the two. You probably also need to sand some on the plastic servo connectors so they fit the header pin spacing. If controlling a lot of servos is needed, the ssc-32 servo controller does a nice job and easy to connect (bit not a "shield" form factor).
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