The plate that I was trying to mesh using mesh generation giving more plate located in node 1 and plate disappeared.
There were two methods of generating mesh: 1) Parametric mesh generator is the preferred method and is best to create this type of mesh using the STAAD.Pro Graphical User Interface
2) The input mesh generation is described is based entirely on commands in the input file alone, and does not have any graphical interface for creation or modification. Please use the first method of Parametric Mesh generator. Created and attached short video showing the process of the same.