How to remove unwanted vertical lines in an Index in Writer

There are strange looking vertical purple squiggly lines being displayed before each header in my contents index in my Libreoffice Writer doc.
They even get printed! And they actually take up space in the document, but you can’t simply select and delete them.
I did not put them there, they look like a line that indicates a spelling error, but in this case they are displayed just before each number of the index.

Before each “header” or before each heading listed in the ToC?
The header is at the top of the page.
Heading styles (Heading 1, etc.) are used to create the ToC.
Just to be sure we are talking about the same thing.

There are two kinds of wavy lines discussed in the Writer guide:

  • blue wavy line = grammar error
  • red wavy line = spelling error
    And these are underlines, not vertical.
    Display of these can be toggled on/off by Shift+F10 (Automatic Spell Checking).

Have you customized the Table of Contents format?

Can you attach (or upload somewhere) a sample of the doc which shows this?

I noticed that they are even displayed in the ‘insert index or table of contents’ menu! I made a screen shot, cant find a way to attach though.

It takes a certain number of posts before you can attach files.
But you can enter URLs …
So upload the image somewhere like Imgur or ??? and post a link.

Can you upload the Writer file somewhere? Or just a sample?

the purple vertical lines do actually appear in the document (they even appear on a printout), how do I get rid of them?

(edit: activated screenshot)

Not sure why, but the image in Imgur is very pixelated.
I can kinda see some lines on the left, but not clearly.
Really going to need a sample file to help you.

I have pinpointed it further, it only occurs when using our standard document style, when I create a new document and insert an index, it does not display the purple vertical squiggly lines before each index item. But then I lose out on the other stuff that is in a standard document, so that is no good.