Win10 64 bit; 24 gigs RAM; third-gen i7 CPU; AMD 7xxx GPU (Crimson ReLive drivers)
Broken: Hash c73206a
Short description of error
When the denoiser processes scenes containing firefly-prone materials and bright highlights, it can lead to results filled with black pixels (some with negative values, others with values of -1.#INDO). Increasing the samples helps to reduce the issue of fireflies going black, but not with highlights that are small and bright.
Exact steps for others to reproduce the error
Open the .blend file, render the scene, and examine the values of the many black pixels on top of Suzanne.