Operating system: Windows 10
Graphics card: ASUS Vega 64 OC Strix (2x)
Broken: 2.8 stable; 2.81, 0d719fcacb3b, 2019-08-11 (Experimental build)
When rendering in Cycles (the error does not occur in EEVEE) with an AMD graphics card the AO map of model parts that use the Principled BSDF shader with a Subsurface value above 0 become shaded improperly. The error is hard to describe so I attached a few screenshots to show the problem. This bug only happens when rendered with an AMD GPU, CPU (here used an AMD Threadripper CPU) and Nvidia CUDA rendering works perfectly fine.
To reproduce that error simply create the monkey head object with a Principled BSDF shader and a Subsurface value above 0 (here I used 0.15) and let it render with the Ambient Occlusion pass enabled and OpenCL. Then, when selecting the AO pass, the error should become visible. To see the error best you could enable GPU + CPU rendering and the AO map should be filled with several squares that looks differently from the rest of the image.