CollabViewer Template navigation issues

Hi everybody, I’m using the CollabViewer template to create an educational VR expereince with an office floor in UE 5.3. Users should be able to explore the space in a multiplayer mode. Hence the collab viewer as basis.
The users should not be able to teleport out of the windows into the courtyard one floor below and they should not be able to teleport on top of furniture. But they can. According to the documentation (Adding Your Own Content to the Collab Viewer in Unreal Engine | Unreal Engine 5.3 Documentation | Epic Developer Community) a NavMesh should work and the sample level that comes with the template should have one. But the sample scene doesn’t and if I create one in my level it does not have any effect.
Any ideas how to fix this?


This is how the NavMesh looks in my editor. It ends at the facade, but I can teleport outside.