Voronoi chunks are children of the particle that is fractured, and thus inherit the parent particle's properties. I see you have a material ID operator in the prior event, which the chunks are inheriting. So the Voronoi operator is setting the cut face ID, then the inherited material ID override is also overriding the chunks.
You can either choose to bake the material ID into the mesh of the first event (choose that option in the Material ID operator), or you can remove the override on the chunk particles by adding a Material ID override to that event and setting the value to 0.
Great, "bake into mesh particles" was it. Thanks
"Override" means just another material ID with "bake into mesh particles" in the voronoi event, I guess.
Adding it without override left some faces black.
But anyway it works with the baking enabled.