Steps to repro:
1. Open the attached project and the scene
2. Press play

Skybox changes don't appear on reflection probes. Obviously reflection probes are fully baked, but the background setting to skybox suggests that I could use a dynamic skybox. Other techniques are blending the current skybox with baked reflections and realtime reflections for dynamic objects. At the moment, changes in the sky aren't visible in reflections and dynamic objects won't be reflected, too.