My shower screen seems to catch when I open/close it. Its an L shape on the bath. It looks like its slipped down at one end as the gap at the bottom is no longer square. When I put a spirit level on ever single edge, including the wall, bath, & screen, its perfectly square. Any ideas? Could it be wooden supports under the corner of the L on the bath behind the side pane is too tight and actually pushing that corner up? You can see in the pic that the gap is nearly gone at the L end.