Steps to reproduce:
1. Download and open the attached project
2. Open scene Assets/1-Comparison Scene/"Scene"
3. Activate Gameobject "2 - Activate this & Bake = Crash"
4. Open the Occlusion window
5. Bake Occlusion data

Result: crash

Reproduced on 5.5.0b11, 5.5.0f1, 5.5.0f3, 5.6.0a3
Not reproduced on 5.3.6p8, 5.4.3p1
Bug first introduced in 5.5

Notes:
-"1 - Activate this & Bake = OK" contains a 10x10x10 occlusion gate, "2 - Activate this & Bake = Crash" contains a 1x1x1 occlusion gate