To reproduce the issue follow the steps:
1. Open Project user have provided
2. Play "10_MagasinGenerale" scene
3. Press L to Reload the scene
Notice that the GI is always identical after reloading the scene
4. Build a standalone Windows player or use the build located in "Lighting Bug/Build"
5. Play the build
Notice the GI after the first load is identical to the scene in the editor
6. Press L to reload scene
Notice that the GI is much brighter after reloading the scene

Reproduced in 5.3.0f4, 5.4.0a6, 5.3.0p1, 5.2.2p4