I have this night scene with fog on a city street. It look good while its noisy but looks horrible when denoised, mostly the fog parts. It looks like there are weird swirls in the fog and I have no idea how to fix this problem.
#Bad Denoising Artifacts with Fog
vapid forge
teal hawk
The noise threshold might be the cause and mess with the denoiser.
If that doesn’t help, look in to multi pass denoising and denoise the combined volumetric layer individually before recombining it with the rest.
(Super image denoiser addon should do the trick)