How can I fix global cell formatting issues in Mac Numbers app?

Does any Numbers user know why, in every cell (50 columns and 342 rows), a large left margin has globally appeared in all cells? Nothing will left-align anymore. All cells are text. And clicking "Center" moves all lines in a cell a character or two to the right. Right justification appears to also move the contents a character or two to the right, but not to the right-hand cell wall. The same happens with Left justification, but one or two characters to the left.

Thank you in advance.

[Re-Titled by Moderator]

Original Title: Mac Numbers "Global" Cell Formatting