Are you sere you use pdfx3 in this case?
Try to use higher version of PDF1.4 or 1.5 during export?
I am pretty sure, eventhough i have to admit, that i wasn't the operator,
but i already contacted him, to get some response on your question & idea:::
Thanks for the reply already:)
I think it is connected to this http://indesignsecrets.com/eliminating-ydb-yucky-discolored-box-syndrome.php
Even, if you work with PNG, in InDesign for print you should use PSD files as PNG does not support color management and only alpha transparency, this is only a selection of transparency what PDF can support.
In InDesign you should in aspect of quality import PDF, AI, PSD and avoid EPS.
thanks for the link! Now i know also the name of the problem,
i hear your advice on the color management.
But also interesting is that our catalogues worked out perfectly for almost 3 years now,
only with pngs...
Anyhow i'll try the workflow explained in the link asap!
PNG isn't really a print format. It stands for Portable Network Graphic.
I'm not surprised you're having issues, as technology evolves it works towards increasing for print files, which can have a negative knock-on effect for non-print files... which isn't surprising either.
You should set up an action to resave the PNGs to Tiff with transparency.
You can then relink all your images to a different extension https://indesignsecrets.com/relink-from-one-image-file-type-to-another.php
We didn't try .tiff-files with alpha channels yet, since our production pipeline is based on png-files, and it worked.
I would test the assumption that the problem is with the .png format before you print again. If you use Acrobat's Object Inspector to check the attributes of a placed .png vs. a .psd or .tiff, Acrobat shows no difference—it doesn't know a png from a tiff.
Here's a PDF/X-3 that includes the same image saved as a PNG-24, PSD, and TIFF and Object Inspector shows them all as DeviceCMYK, 32-bits, at 291ppi. It could be that something about the output of transparency in general has change at the press. You might look at exporting to the Adobe recommended PDF/X-4 rather than X-3