The file format should not matter, assuming the geometry is intact… unfortunately there seem to be some issues with your navmesh geometry, the triangulation has not happened correctly:
Each square along the path is a separate mesh, containing 4 triangles, and 2 triangles are stacked on top of the other 2. The navmesh should all be one single mesh, with continuously connected triangles.
If you could share the original file you used to create this navmesh I can help more.