Reproduction steps:
1. Open the attached project "Additive Loading Testing.zip";
2. Open the "CameraScene.unity" scene;
3. Enter a play mode and click on the button "Load Scene One (Additive)";
4. Close the play mode and repeat 3 step, but now press the "Load Scene One (Single)" button.

** This occurs when using real-time lighting along with baked GI via the light probes

Expected results: Light probes will be loaded correctly using both additive or normal scene loading.
Actual results: the scene is loaded differently.

Reproduced on: 5.6.2p4, 2017.1.0p2, 2017.2.0b4, 2017.3.0b9, 2018.1.0a5.
Not reproduced on: 5.5.3p3.
Regression has started: 5.6.
Tested on both DX9 and DX11.