How to remove brown dashed lines in Word whose purpose is to show that something is wrong about the formatting?

Please note that I already read all related questions, but my issue is different.

I have in some Word documents brown dashed lines across some paragraphs, which apparently come to notify that something is wrong with the formatting there, because when I change the font size of part of a paragraph I get these lines there. This is happening only to some files. When I convert it to a PDF those lines disappear.

Any idea how to get rid of it?

Here is a screenshot: