Shadows being almost completely removed

Hi, I think I might be experiencing a bug. When I open my old file that rendered correctly last week, the shadows are perfect but if I click on almost anything, the render preview changes in the canvas and my shadows disappear. I've even rendered a few times with different shadow opacities and they all come out the same so I know there is something going on. Please help!

How the render should look:

the new render even though I've changed nothing.