Not sure on area.

When there is no baked occlusion in the scene the lighting will flicker and areas will turn un-lit in blocked areas. When occlusion is baked then the scene will mostly be fine except a few objects which are not marked as static.

steps to repo
1. Open attached project.
2. Load Demo1 scene
3. Hit play and move around with WSAD and Mouse.
4. Observe lighting.
5. Open occlusion window. If occlusion is baked already, clear it and re-observe, if it's not, bake occlusion with default settings and re-observe.

Tested in 5.4 and 5.3 both reproduces. Will test on 5.1 and edit.