Tom, something is wrong when six screws come loose at the same time. A screw is like a spring. Tightening it stretches it and the tension holds it tight. The tension stress must be within the elastic limits of the screw metal - and this tension includes the load placed on screw. In other words, the tension must not be great enough to permanently stretch the screw. The stretched screw comes loose.
Examine your screws closely under magnification. Are they stretched? If so, the repair must include some way of reducing the tension on the screws or using screws that can withstand more tension.