Hello! Glad to see that the info is working!
Regarding the NavMeshBoundVolume for it to cover all parts of the shape, you can modify the max simplification error to super high and fix that issue. you can find it in the RecastNavMesh-Default that should be in your outliner.
The character no longer moving are you sure you only changed the mesh without deleting any of the mannequin functionality? The following video shows how to replace the mesh of the mannequin without breaking functionality:
hopefully that works, let me know if it works!