Happens on new projects too.
New blueprint class > actor > add box collision > add nav modifier = Nav mesh won’t change until you change the collision settings of the components.
For the crash it seems to be caused by changing the collison settings, toggling the “Can Ever Affect Navigation” on/off and moving a component. I also get the semi permanent holes in the navigation bug when I do this, where if I set the collision so the navigation mesh rebuilds and toggle the “Can Ever Affect Navigation” to off and move the blueprint. The hole that was built by the moved mesh will be kept there until I restart the project.