I have few SSRS Reports that is show/hide columns based on the parameter. Some time you may get White Space due to hidden column. The reason behind the white space is, The design which you made you are changing the HIDDEN property to Header and Data Row. It means you made hidden only Header and Data row. But you can see the Tablix row at the top of your Header and Data row which is in Grey Color. So right click the particular Tablix Row and Custom Invisible Property Set True or False.
SSRS White Space due to Hidden Column ?