Steps to reproduce:

1. Download the attached project and open TestScene01
2. In the Lighting Settings window make sure that Ambient Occlusion is enabled and both Direct and Indirect contribution sliders are at 1
3. Bake the scene lighting
4. Note that the scene is void of any direct AO
5. Tweak the Max Distance value and rebake the scene
6. Note that the direct AO is now present

Notes:
Repro : 2019.1a6, 2018.3.0b9
Not repro on 2018.2.2f1

If I first start up Unity and have AO turned on and clear everything and make a fresh bake, the AO is almost non-existing.
If I then turn AO off, clear, bake, turn on, bake, then it will look fine. I have been debugging this for days, and thats the only way for me to get AO to work again for me. I have tried moving the objects around, clearing cache etc, but toggling it is the only thing working. Not sure whats going on

1b is after startup, clearing of cache and a bake
2b is fresh bake without AO
3b is fresh bake with AO

Nothing else has changed.

Using this build: https://katana.bf.unity3d.com/projects/Unity/builders?unity_branch=lighting%2Fdenoiser-export-textures