System Information
Operating system: Windows 8.1
Graphics card: NVIDIA GeForce GT 620M

Blender Version
Broken: 2.80, e4dbfe0a98c1, blender2.8, 2018-12-27

Short description of error
The cryptomatte passes are not rendering while the save buffers option is enabled.

Exact steps for others to reproduce the error

1. Enable cycles.
2. Go in the render tab to performance -> final render and enable save buffers.
3. Enable the cryptomatte passes in the view layer tab.
4. Render the current frame and try to read the render passes with the cryptomatte node in the compositing editor.