Hi,
I can get the same behaviour when testing. This is not solved by putting 'Serialize Default Values' to Yes. See attached oml.
Obviously, when using SerializeJSON, there is no metadata available, so the Datagrid component has to figure out what columns it should generate. Apparently it looks only at the first row of data to do this, and apparently, a piece of data with the value "" leads to a whole column not being shown. I think both are poor choices, and if DataGrid endorses being used in combination with json serialize, this could be considered a bug.
That being said, @Hamza Gulzar , why not make use of the ArrangeData action, why are you saying that you can not use it ?? If your truly can't use it, I guess an option would be to manually mimic it, by adding the metadata to the result of the Serialize action...but that's an ugly option in my opinion. (see grid 4 in example oml.)
Dorine
P.S.
@Hamza Gulzar when sharing an oml to demonstrate a problem, please pay attention to dependencies, your oml could not be implemented because it has dependencies to a theme and a sample module.