Suddenly rendering a double image The render (cycles) seems to be rendering the scene twice, slightly enlarging one image, and superimposing it in the same render result. The result I'm getting is as if seeing double. I have only one render layer, one scene, one camera. Test renders worked fine until I added a denoise mode in the compositor and moved the camera, and now I can't remove the effect, even by replacing the camera.

Incidentally, I tried switching to eevee just to see what happens; it renders only the HDRI and nothing else. This is even more perplexing.

Sorry if this sounds terse. I meant go to go bed two hours ago and I'm frustrated I can't render this overnight now.
I found out the problem: I have fluid simulation in the scene, and the camera was reflecting off the domain's bounding box. The simulation only kicks in partway, and I forgot that this would cause the domain to resemble a watery cube prior to that point.