Bug 1 
Navmesh is not being generated on brush components. I have a couple testing levels where I use brush boxes for floors. I checked the different levels and it is only generating on static meshes. I double checked and it is working in 5.4.4.
5.5
5.4.4
Bug 2
SpawnDecalAttached causes dynamic Navmesh to rebuild.
This was also OK in 5.4.4
Here is a video showing the bugs.
