It can happen that the created texture has some “black islands”. It is the result of the unwrap settings. The factor that makes changes to this effect is the Unwrap, specifically its utilization.
Select a model in RC …
https://dev.epicgames.com/community/learning/knowledge-base/a3Gz/capturing-reality-i-see-an-empty-space-in-my-created-texture-what-is-it-and-why-is-it-there