Columns appearing from nowhere, formatting going weird

[Noone_Important]

I have a 9,000 page Word document I have created by scanning PDFs using OCR and for the most part I have been content to clean it up a bit by hand. The OCR didn't do a great job, but it was OK.

About 4,000 words in though and the and suddenly the text seems to be divided into columns. I can't see that there is any table screwing with the formatting (although occasionally throughout the document unnecessary tables have been created).

I have highlighted some of the text (below). 

Is there any easy fix for this? I can't cut and paste text without it getting worse, and even if I try to Paste it into the document without formatting it still seems to end up in columns.

[#2]

@Noone_Important 

Is this Word for Windows? Click the ¶ icon on the Home tab to display nonprinting marks. Maybe the text is in fact in newspaper columns, separated by section breaks?

Another possibility is that some of the text has ended up in text boxes, which sometimes happens when OCR software is trying to recreate the appearance of the original file.

[#3]

Thanks @Stefan_Blom. You may be right about the section breaks. It is weird that it would start happening on every page, when I have gone 4,500 pages without this happening at all.

How can it be fixed?

Sometimes though it seems to add columns, as per the below. 

Then if I try to delete the section break, I end up with this:

[#4]

@Noone_Important Before deleting the Section Break, select the text that is in columns and go to the Layout tab of the ribbon and in the Page Setup section, click on the Columns dropdown and then click on One