I first noticed this when I recently exported a file to PDF. I have just started working on a new document and the white 'stroke' lines are now appearing on screen even before I export.
I have checked the stroke settings and this is set to 'off'.
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Looks like the stroke is part of the file you are linking to. In which case you need to edit that actual link and remove the stroke then update the link.
You may consider restoring all preferences and default settings: