Those lines may just be PDF artefacts and may not print. To check this, open the PDF proof in Adobe Reader and click Ctrl + K on your keyboard which will bring up preferences.
On the preferences pop up, go to page display and un-tick smooth line art and smooth images and then click ok. If the lines no longer show on your PDF proof, they will not print as they’re just artefacts. (Once you've done this, remember to tick those options so they're back on.)
If the lines don’t disappear, it could be a flattening issue. If you can supply your artwork as either a PDF X1a file format or as a high-resolution JPG file then this will help.
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