Operating system: Windows 10, Ubuntu Linux 18.04
Graphics card: Geforce GTX 1060, Geforce RTX 2060
Broken: Blender 2.79.7 - April 13., 2.80 Beta - April 14.
Cycles GPU does need recalculate the Multiple Importance Map with HDRi after modifying a material. For some reason Octane and mostly other render engines doesn't need that. When it's a bug or not that makes it unreasonably difficult the shading process.