Netrender addon issue


Yesterday I started a network animation rendering job using the Network Renderer addon.
In the beginning it looked great but it stopped producing images sometime during the night. My suspect is a Windows update which must have made one of the slaves reboot, so eventually stopping the job. It seems very unstable, one slave falls out, the whole stops, even though the computers continue to work on 100% CPU load.

But my greatest issue is with the rendered images themselves because a lighting inconsistency occurred.
The farm consists of six computers, 3i7-4770 and 3i7-4790, so basically the same power, with 16-32 GB RAM (only ~6 is used for the render). One was only master, five slaves of which one was the client.
The model is a cave system, separated into 10 model files for quick turning on-off the visibility of certain parts, and these are linked into a master file that has the cameras, lights, settings.
The client/slave computer produced good images, but the rest was too light, like if the environment strength would have been multiplied.

Have anyone encountered this before or have some idea what caused it?