Thank you, Dave!

That did the trick.

"Dave O" wrote:

Most likely you've inadvertenly hidden columns, rather than lost them.
When you look at the visible columns, say A and C, is the vertical line
between A and C heavier than the separator between C and D?

Try this: highlight columns A through C by left-clicking on A and
dragging over to C. Then right-click the selection and select UnHide
from the menu. B should then appear.