Did you select the entire brush when you created those displacements? If so, you'll have extra unseen faces attached to these displacements that the compiler will still attempt to light, resulting in these visible shadows.
The texture application tool
can be used to avoid or fix this. With this tool open, you can select individual faces (or multiple with ctrl pressed) and create displacements from only those faces. Similarly, you can select any displacement faces you don't need and destroy them from the Displacement tab. If you destroy all displacements from a given brush, you will get the base brush back.