Trying to create a table but letters are aligned vertically

[Bosa]

If I merge 2 cells the problem is fixed, but doubling the amount of columns and merging pairs causes the problem to return.

[EarnestAl]

Do you want the letters next to each other? Add something in step 2. if you do.
You really need to turn on formatting marks (View > Formatting marks). I presume that there is a paragraph mark, ¶ , between each letter. Find and Replace (Ctrl+H) can easily remove paragraph marks.
Select the table, click Edit > Find and Replace, in the dialogue box that opens:

1. In Find enter $
2. In Replace leave it empty
3. Tick Current selection
4. Tick Regular Expressions

Then click Replace all

If you have line breaks, ↵ , instead of paragraphs then in step 1, instead of $, enter \n

[LeroyG]

Check the Padding values and/or check the After text Indent.

LibreOffice 7.1.8.1.

[Bosa]

Thank you so much, After Text had been set to 1", set it down to 0 and it fixed it!