When a Static Mesh is reimported with a different vertex count than the number of vertex colors on the instance, you get errors like this in map checks and during cooking:
StaticMeshActor_73 (LOD 0) has hand-painted vertex colors that no longer match the original StaticMesh
When instanced vertex colors are mismatched against the original Mesh's vertices, it makes the vertex colors look wrong on a PC; on consoles the vertex colors simply do not exist. To correct that, you can use the Fix tool in the Mesh Paint Toolbar to fix vertex colors if they do not match up with the original Static Mesh Asset.
This feature will only be available if a Mesh needs fixing; otherwise, it is disabled. The tool works well most of the time, especially when you are only making small changes. The more extreme your changes to the Mesh are, the more likely that the colors will not match. The feature is designed to always match some color, even if the changes are drastic. The reason this tool is not automatic is because that would prevent people from easily reversing the fix if they did not like the results. Additionally, adding the feature to Mesh Paint Mode means you can easily perform minor changes after the fix is applied.
