win7 x64, Vega 64, driver 17.9.1
Broken: latest master since a week at least
Short description of error
After rendering for some seconds with BPT, the gpu idles, but the tile will never finish.
Exact steps for others to reproduce the error
Render this scene from barbershop (10_03_B - Agent dodges) https://cloud.blender.org/p/agent-327/591ac3cabb3ea141675bbaf2 with OpenCL, the first tile will render for 1-2 seconds with 100% GPU usage and then go idle, never finishing it.