I am rendering out several layers at a high resolution, running them through the Denoise Node, and then outputting them with the File Output node. I have some passes that are getting denoised, and some that are not.
After the render runs, the output folder contains images for each pass plugged into the output node, but all the ones that go through a Denoise are just black. While the compositor runs, I can see the files get created. It finishes creating all the outputted files before the denoise nodes finish running, as they are quite slow on 4k images. By the time the denoise finishes, the file output node has already run, and it does not run again. If I disable the denoise nodes, everything outputs just fine (but is, of course, noisy.)
I've tried turning off Two Pass in the compositor options, but it doesn't help. Is there any way to fix this? Is this a bug that I should report, or a limitation?
EDIT: It looks like this problem can happen when saving an image on its own. When you open the save file dialogue, it will trigger the compositor to run again. If you don't wait for it to finish running the denoise node before hitting save, your save file will be blank.