How to show hidden columns

1. Find hidden columns

Find the place where the columns were hidden. You can recognize it by a jump in the enumeration of the column headers:

2. Mark surrounding columns

Select the two columns surrounding the affected hidden column.

3. Show

Right-click one of the two columns and select "Show".

Important: Repeat this for all attribute sets, if columns are missing there as well.

How you can now hide columns that you may no longer need, you will learn here.