I have updated to the beta version of Astar, and now it is complaining about read/write:
“Some mesh collider meshes could not be included when scanning the graph because they are marked as not readable. This includes the mesh ‘Room2’. You need to mark the mesh with read/write enabled in the mesh importer.”
Note that I only have “Rasterize Colliders” enabled, not meshes, which is what is referenced here: Do Meshes have to be Read/Write enabled?