(example: 2.79b release)
(example: 2.80, edbf15d3c044, blender2.8, 2018-11-28, as found on the splash screen)
Mac Pro 2013, Using External GPU Amd Rdeon RX580.
In the rendeing process using Cycles, i Activate the Desnoising option in "View Layer". The resulting image has "Black" boxes where the GPU denoise worked, not happen when use only CPU. This has been happenig in the olds 2.8 alpha versions.
I´m Render using GPU + CPU