Try resetting the panel and if necessary, reset grid preferences (you may want to take screenshots or record current grid column order first though).  This is on a user by user basis.

Should I do this on the header tab or the lines tab where I want it to keep my columns and column widths, or does it not matter which tab I am on?

It doesn't matter.  Resetting all grids will reset the grid customizations for your workstation and user for that particular task.  Resetting the panel size and position also resets for your user for that particular task but it really just resets the last saved size and position.  I suspect the grids is what you need to reset but if you are in a VDI environment, this won't likely won't help much besides restoring to the default grid settings.

It doesn't matter.  Resetting all grids will reset the grid customizations for your workstation and user for that particular task.  Resetting the panel size and position also resets for your user for that particular task but it really just resets the last saved size and position.  I suspect the grids is what you need to reset but if you are in a VDI environment, this won't likely won't help much besides restoring to the default grid settings.

I should add that the reset only occurs for that particular task you perform the reset from.