Roof Catch Movement

[Curdster]

Any advice. I have started to notice that the roof catch plate screwed into the top centre of the windscreen surround has started to move at an angle thus causing the hinged clip on the actual roof to slide to one side.
Is this common and if so hwo can I fix. I have taken our the two Allen bolts, checked that the plate is not bent, which it is not, then refitted. However a few drives later and the whoel thing has moved again!