Could you please post a screenshot to illustrate the issue?
I assume it is a PDF/X-1a or PDF/X-3, please try using an PDF/X-4 (created from the source file, not converted from the existing pdf) instead.
No, the screenshot has seemingly been down sampled to 889px x 679px and does not indicate the criticised behaviour at all.
Once again: Please try using a proper X-4 pdf instead of the other kinds.
White lines in converted pdfs usually indicate that flattening has occurred.
One alternative might applying Layer > Layer Mask > From Transparency and dismissing the Layer Mask – but that only helps in certain cases.