Strange blue lines in editor

I have a similar problem.

Show Invisibles reveals double blue lines (screenshot). How do I remove them?

I have split your post to a new topic; for the sake of trivial this doesn’t have anything to do with page breaks, section breaks or compiling.

You have a table (or many) in your editor. Just right-click anywhere in the rectangular areas and choose the “Remove Table” command from the table submenu. Might be a good idea to check around throughout your text with invisibles on. If one sneaked in, there may be others. These usually come in when pasting from old or poorly formatted websites.