Post Process Layer not working on Main Camera

Hi, I've been working on my film for quite a while now. Same setup as for months, but today my main camera is not showing my post process layer in the camera preview anymore.

Basically, I open my scene, I see in my Scene and Game view that everything is fine, I see my ambient occlusions, depths of field etc etc. I click on main camera, in its little camera preview window, none of the post process effects are visible. I untick/tick my post process layer, it seems to work fine, but doesn't affect the camera preview at all, just the scene and game view.

I press play, my film doesn't play, my main camera doesn't follow my timeline with all the cinemachine virtual cameras I've set up to make my shots. It's stuck in one place. I stop, and when I go back to scrubbing in my timeline, my scene view, and my game view, now don't show any of the post process effects also.

I've got two timeline (director group), one to make my shots, the second to make the montage of my film so it's easier to move things around.

I can't get my head around it. I can't code at all (in case you have a solution involving coding).