After some time, wires can become loose due to heat (expansion/shrinking) or from children stepping directly on the wires.
The wires can be tightened by hand.
First you must undo the two nuts which are on both sides of the bottle screw.
Next tighten the bottle screw by turning it clockwise. When you feel that it can’t go anymore and the wire is taut, return the nuts to their original position to hold the bottle screw in place.