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'.

[![enter image description here](https://i.stack.imgur.com/EIlz9.png)](https://i.stack.imgur.com/EIlz9.png)