Black Lines when Exporting to PDF

[Annie2]

When I export to PDF for print with printers marks, bleed etc, I am seeing black vertical 'border-type' lines on some of the pages.  There are no black borders showing on the document in AD.  Any idea how I can get rid of these?  Many thanks

  

[MEB]

Hi Annie2,

Welcome to Affinity Forums

Can you please upload your .afdesign file using this link so we can take a look? All files will be deleted after being inspected.

Thanks.