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Could it be an inherent design flaw
If the threadings in the screw are in the same direction as the barrel uncoupling movement, it will eventually loosen.
Not sure if i can illustrate this well. One barrel turns clockwise, and the other barrel turns anti-clockwise. Therefore, the uncoupling of the clockwise turning barrel will be ok, but the other anticlockwise turning barrel will undo the screw. This is if the screws used have the same threading direction.