Errors in Running the client
In Editor press P to see the navigation mesh
In game use console -> show navigation
If you dont see the navigation mesh, try to edit the size slightly, and it will automatically recalculate it. There is no need to do "Calculate Navigation Paths".
I had these in my DefaultEngine.ini and were causing the problem:
[/Script/NavigationSystem.RecastNavMesh] AgentMaxSlope=69.428574 AgentMaxStepHeight=78.338669 CellHeight=1.000000 AgentMaxHeight=400.000000 RuntimeGeneration=Dynamic bDrawPolyEdges=True
I left only this one and it started to work:
RuntimeGeneration=Dynamic
I had a problem where the sewer level was imported as a single object and the collition mesh was very big, this was messing up the navmesh calculations, and so a "fictional" roof was created, this made my character walk on an invisible roof in game. I had to change the sewers mesh to have "Use complex collision as simple".