Hello all, I am using Unity 2017.1.0b2, I realized this problem in a few versions, but I just found out where.
After a lot of debugging, I realized the the AO from the Stack post processing has a huge problem on Shadowmask mixed lightings.
It simply pass through all static object and only renders what is not. So the tree and a door are real time, these are the only objects it renders on.
When I use subtract or no lightmap mode, it works perfectly
Hope it helps.
Bests
