I have a seemingly simple problem.
I create a new adjustment layer and ensure it is the first layer on top of the other content layers.
No matter what effect I apply to it, it has no effect on the video in the preview window.
Applying effects to the actual content layers shows the effect in the preview window. Doing so to adjustment layer doesn't seem to work.
Show us screenshots! On a first guess I would say you have set your adjustment layer to also be a guide layer, which of course is non-rendering.
I think I figured it out.
The problem is when I have a composition comprising multiple layers, one from each multi-pass channel from a 3D program animation brought it into after affects and extracted into individual layers. Putting an adjustment layer on top does seem to work.
The alternative is to first pre-composite the individual multi-pass channel layers after done working with them and then throwing an adjustment layer on top of the single pre-composite layer.