Version 6 guidelines only shows when saving a file

I recently upgraded to version 6 which has guidelines that you can use for framing an object. I have noticed when I go to save a file the thumbnail is just a horizontal guideline. The file is okay but the thumbnail is the problem. How can I correct that? Thanks

I think that’s because guidelines are currently treated as normal objects that just have a huge (but endless) size. Since the line is the dominant object then, it might be the only element visible in the thumbnail (because all other objects are just 0.0001% (I don’t know the actual ratio, just as an idea) in size compared to the line).