Exporting to PDF images not all showing, randomly


I have created 9 boxes on a sheet in Corel, within these boxes are some blended colours and on-top of that an image, when exported some of the images show and some don't (the exact same image, an exact duplicate.

To troubleshoot I exported just the images and that was fine, just the boxes without images was fine,but here is where it really confuses me.

I export to PDF the top three boxes (9 in a sheet), and boxes 1 and 3 have the image, but 2 doesn't

I export to PDF the whole sheet and now boxes 1 and 3 have no image but 2 does!!

I hope i've explained correctly and someone can help, this is really causing me some problems.