I’d wager thats a rendering bug rather than the actual nav mesh not working.
Try it.
Make an actor with AI that goes to the mouse click, and click in the area that should be red to see if he gets stuck on the cube or not.
It’s very possible they broke those too, so if it doesn’t stop the actor from moving (and even if it does, since rendering is busted) you may want to consider opening up a bug report…